diff --git a/common/libeval_compiler/libeval_compiler.cpp b/common/libeval_compiler/libeval_compiler.cpp
index 7981db98d9..3c6b934feb 100644
--- a/common/libeval_compiler/libeval_compiler.cpp
+++ b/common/libeval_compiler/libeval_compiler.cpp
@@ -223,7 +223,7 @@ void COMPILER::parseOk()
 }
 
 
-bool COMPILER::Compile( const std::string& aString, UCODE* aCode )
+bool COMPILER::Compile( const std::string& aString, UCODE* aCode, CONTEXT* aPreflightContext )
 {
     // Feed parser token after token until end of input.
 
@@ -238,7 +238,7 @@ bool COMPILER::Compile( const std::string& aString, UCODE* aCode )
     if( aString.empty() )
     {
         m_parseFinished = true;
-        return generateUCode( aCode );
+        return generateUCode( aCode, aPreflightContext );
     }
 
     do
@@ -265,7 +265,7 @@ bool COMPILER::Compile( const std::string& aString, UCODE* aCode )
         }
     } while( tok.token );
 
-    return generateUCode( aCode );
+    return generateUCode( aCode, aPreflightContext );
 }
 
 
@@ -592,7 +592,7 @@ void COMPILER::setRoot( TREE_NODE root )
 }
 
 
-bool COMPILER::generateUCode( UCODE* aCode )
+bool COMPILER::generateUCode( UCODE* aCode, CONTEXT* aPreflightContext )
 {
     std::vector<TREE_NODE*> stack;
     std::set<TREE_NODE*>    visitedNodes;
@@ -689,22 +689,22 @@ bool COMPILER::generateUCode( UCODE* aCode )
                     }
 
                     // Preflight the function call
-                    CONTEXT ctx;
-                    VALUE*  param = ctx.AllocValue();
+                    VALUE*  param = aPreflightContext->AllocValue();
                     param->Set( node->value.str );
-                    ctx.Push( param );
+                    aPreflightContext->Push( param );
 
                     try
                     {
-                        func( aCode, &ctx, vref );
+                        func( aPreflightContext, vref );
+                        aPreflightContext->Pop();           // return value
                     }
                     catch( ... )
                     {
                     }
 
-                    if( ctx.GetErrorStatus().pendingError )
+                    if( aPreflightContext->GetErrorStatus().pendingError )
                     {
-                        m_errorStatus = ctx.GetErrorStatus();
+                        m_errorStatus = aPreflightContext->GetErrorStatus();
                         m_errorStatus.stage = ERROR_STATUS::CST_CODEGEN;
                         m_errorStatus.srcPos = node->leaf[1]->leaf[0]->srcPos + 1;
                         return false;
@@ -780,14 +780,14 @@ bool COMPILER::generateUCode( UCODE* aCode )
 }
 
 
-void UOP::Exec( CONTEXT* ctx, UCODE* ucode )
+void UOP::Exec( CONTEXT* ctx )
 {
     switch( m_op )
     {
     case TR_UOP_PUSH_VAR:
     {
         auto value = ctx->AllocValue();
-        value->Set( reinterpret_cast<VAR_REF*>( m_arg )->GetValue( ucode ) );
+        value->Set( reinterpret_cast<VAR_REF*>( m_arg )->GetValue( ctx ) );
         ctx->Push( value );
     }
         break;
@@ -798,7 +798,7 @@ void UOP::Exec( CONTEXT* ctx, UCODE* ucode )
 
     case TR_OP_METHOD_CALL:
         //printf("CALL METHOD %s\n" );
-        m_func( ucode, ctx, m_arg );
+        m_func( ctx, m_arg );
         return;
 
     default:
@@ -866,15 +866,13 @@ void UOP::Exec( CONTEXT* ctx, UCODE* ucode )
 }
 
 
-VALUE* UCODE::Run()
+VALUE* UCODE::Run( CONTEXT* ctx )
 {
-    CONTEXT ctx;
-
     for( UOP* op : m_ucode )
-        op->Exec( &ctx, this );
+        op->Exec( ctx );
 
-    assert( ctx.SP() == 1 );
-    return ctx.Pop();
+    assert( ctx->SP() == 1 );
+    return ctx->Pop();
 }
 
 
diff --git a/include/libeval_compiler/libeval_compiler.h b/include/libeval_compiler/libeval_compiler.h
index 765e3c0705..2d31990f92 100644
--- a/include/libeval_compiler/libeval_compiler.h
+++ b/include/libeval_compiler/libeval_compiler.h
@@ -249,7 +249,7 @@ class VAR_REF
 {
 public:
     virtual VAR_TYPE_T GetType() = 0;
-    virtual VALUE GetValue( UCODE* aUcode ) = 0;
+    virtual VALUE GetValue( CONTEXT* aCtx ) = 0;
 };
 
 
@@ -304,14 +304,14 @@ private:
 class UCODE
 {
 public:
-    typedef std::function<void( UCODE*, CONTEXT*, void* )> FUNC_PTR;
+    typedef std::function<void( CONTEXT*, void* )> FUNC_PTR;
 
     void AddOp( UOP* uop )
     {
         m_ucode.push_back(uop);
     }
 
-    VALUE* Run();
+    VALUE* Run( CONTEXT* ctx );
     std::string Dump() const;
 
     virtual VAR_REF* createVarRef( COMPILER* aCompiler, const std::string& var,
@@ -344,7 +344,7 @@ public:
         m_func( std::move( func ) )
     {};
 
-    void Exec( CONTEXT* ctx, UCODE *ucode );
+    void Exec( CONTEXT* ctx );
 
     std::string Format() const;
 
@@ -428,7 +428,7 @@ public:
 
     void setRoot( LIBEVAL::TREE_NODE root );
 
-    bool Compile( const std::string& aString, UCODE* aCode );
+    bool Compile( const std::string& aString, UCODE* aCode, CONTEXT* aPreflightContext );
     void ReportError( const wxString& aErrorMsg );
     ERROR_STATUS GetErrorStatus() const { return m_errorStatus; }
 
@@ -441,7 +441,7 @@ protected:
 
     LEXER_STATE m_lexerState;
 
-    bool generateUCode( UCODE* aCode );
+    bool generateUCode( UCODE* aCode, CONTEXT* aPreflightContext );
 
 
     /* Token type used by the tokenizer */
diff --git a/pcbnew/drc/drc_rule.cpp b/pcbnew/drc/drc_rule.cpp
index 22dbdd50d2..7ffe21625e 100644
--- a/pcbnew/drc/drc_rule.cpp
+++ b/pcbnew/drc/drc_rule.cpp
@@ -89,6 +89,9 @@ DRC_RULE* GetRule( const BOARD_ITEM* aItem, const BOARD_ITEM* bItem, int aConstr
         {
             if( rule->m_Condition.EvaluateFor( aItem, bItem ) )
                 return rule;
+
+            if( bItem && rule->m_Condition.EvaluateFor( bItem, aItem ) )
+                return rule;
         }
     }
 
@@ -113,9 +116,10 @@ bool DRC_RULE_CONDITION::EvaluateFor( const BOARD_ITEM* aItemA, const BOARD_ITEM
     BOARD_ITEM* a = const_cast<BOARD_ITEM*>( aItemA );
     BOARD_ITEM* b = aItemB ? const_cast<BOARD_ITEM*>( aItemB ) : DELETED_BOARD_ITEM::GetInstance();
 
-    m_ucode->SetItems( a, b );
+    PCB_EXPR_CONTEXT ctx;
+    ctx.SetItems( a, b );
 
-    return m_ucode->Run()->AsDouble() != 0.0;
+    return m_ucode->Run( &ctx )->AsDouble() != 0.0;
 }
 
 
@@ -126,7 +130,9 @@ bool DRC_RULE_CONDITION::Compile()
     if (!m_ucode)
         m_ucode = new PCB_EXPR_UCODE;
 
-    bool ok = compiler.Compile( (const char*) m_Expression.c_str(), m_ucode );
+    PCB_EXPR_CONTEXT preflightContext;
+
+    bool ok = compiler.Compile( (const char*) m_Expression.c_str(), m_ucode, &preflightContext );
 
     if( ok )
         return true;
diff --git a/pcbnew/pcb_expr_evaluator.cpp b/pcbnew/pcb_expr_evaluator.cpp
index 5f5b930497..8c3dadbfed 100644
--- a/pcbnew/pcb_expr_evaluator.cpp
+++ b/pcbnew/pcb_expr_evaluator.cpp
@@ -30,7 +30,7 @@
 
 
 
-static void onLayer( LIBEVAL::UCODE* aUcode, LIBEVAL::CONTEXT* aCtx, void *self )
+static void onLayer( LIBEVAL::CONTEXT* aCtx, void *self )
 {
     LIBEVAL::VALUE* arg = aCtx->Pop();
     LIBEVAL::VALUE* result = aCtx->AllocValue();
@@ -54,14 +54,14 @@ static void onLayer( LIBEVAL::UCODE* aUcode, LIBEVAL::CONTEXT* aCtx, void *self
     }
 
     PCB_EXPR_VAR_REF* vref = static_cast<PCB_EXPR_VAR_REF*>( self );
-    BOARD_ITEM*       item = vref ? vref->GetObject( aUcode ) : nullptr;
+    BOARD_ITEM*       item = vref ? vref->GetObject( aCtx ) : nullptr;
 
     if( item && item->IsOnLayer( layer ) )
         result->Set( 1.0 );
 }
 
 
-static void isPlated( LIBEVAL::UCODE* aUcode, LIBEVAL::CONTEXT* aCtx, void *self )
+static void isPlated( LIBEVAL::CONTEXT* aCtx, void *self )
 {
     LIBEVAL::VALUE* result = aCtx->AllocValue();
 
@@ -69,7 +69,7 @@ static void isPlated( LIBEVAL::UCODE* aUcode, LIBEVAL::CONTEXT* aCtx, void *self
     aCtx->Push( result );
 
     PCB_EXPR_VAR_REF* vref = static_cast<PCB_EXPR_VAR_REF*>( self );
-    BOARD_ITEM*       item = vref ? vref->GetObject( aUcode ) : nullptr;
+    BOARD_ITEM*       item = vref ? vref->GetObject( aCtx ) : nullptr;
     D_PAD*            pad = dynamic_cast<D_PAD*>( item );
 
     if( pad && pad->GetAttribute() == PAD_ATTRIB_STANDARD )
@@ -91,17 +91,17 @@ PCB_EXPR_BUILTIN_FUNCTIONS::PCB_EXPR_BUILTIN_FUNCTIONS()
 }
 
 
-BOARD_ITEM* PCB_EXPR_VAR_REF::GetObject( LIBEVAL::UCODE* aUcode ) const
+BOARD_ITEM* PCB_EXPR_VAR_REF::GetObject( LIBEVAL::CONTEXT* aCtx ) const
 {
-    const PCB_EXPR_UCODE* ucode = static_cast<const PCB_EXPR_UCODE*>( aUcode );
-    BOARD_ITEM*           item  = ucode->GetItem( m_itemIndex );
+    const PCB_EXPR_CONTEXT* ctx = static_cast<const PCB_EXPR_CONTEXT*>( aCtx );
+    BOARD_ITEM*             item  = ctx->GetItem( m_itemIndex );
     return item;
 }
 
 
-LIBEVAL::VALUE PCB_EXPR_VAR_REF::GetValue( LIBEVAL::UCODE* aUcode )
+LIBEVAL::VALUE PCB_EXPR_VAR_REF::GetValue( LIBEVAL::CONTEXT* aCtx )
 {
-    BOARD_ITEM* item  = const_cast<BOARD_ITEM*>( GetObject( aUcode ) );
+    BOARD_ITEM* item  = const_cast<BOARD_ITEM*>( GetObject( aCtx ) );
     auto        it = m_matchingTypes.find( TYPE_HASH( *item ) );
 
     if( it == m_matchingTypes.end() )
@@ -264,16 +264,18 @@ PCB_EXPR_EVALUATOR::~PCB_EXPR_EVALUATOR()
 
 bool PCB_EXPR_EVALUATOR::Evaluate( const wxString& aExpr )
 {
-    PCB_EXPR_UCODE ucode;
+    PCB_EXPR_UCODE   ucode;
+    LIBEVAL::CONTEXT preflightContext;
 
-    if( !m_compiler.Compile( (const char*) aExpr.c_str(), &ucode ) )
+    if( !m_compiler.Compile( (const char*) aExpr.c_str(), &ucode, &preflightContext ) )
     {
         m_errorStatus = m_compiler.GetErrorStatus();
         return false;
     }
 
 // fixme: handle error conditions
-    LIBEVAL::VALUE* result = ucode.Run();
+    LIBEVAL::CONTEXT ctx;
+    LIBEVAL::VALUE*  result = ucode.Run( &ctx );
 
     if( result->GetType() == LIBEVAL::VT_NUMERIC )
         m_result = KiROUND( result->AsDouble() );
diff --git a/pcbnew/pcb_expr_evaluator.h b/pcbnew/pcb_expr_evaluator.h
index 1b0aefd2f8..aeeed1a108 100644
--- a/pcbnew/pcb_expr_evaluator.h
+++ b/pcbnew/pcb_expr_evaluator.h
@@ -40,18 +40,23 @@ class PCB_EXPR_VAR_REF;
 class PCB_EXPR_UCODE : public LIBEVAL::UCODE
 {
 public:
-    PCB_EXPR_UCODE()
-    {
-        m_items[0] = nullptr;
-        m_items[1] = nullptr;
-    }
-
     virtual LIBEVAL::VAR_REF* createVarRef( LIBEVAL::COMPILER *aCompiler,
                                             const std::string& aVar,
                                             const std::string& aField ) override;
 
     virtual FUNC_PTR createFuncCall( LIBEVAL::COMPILER* aCompiler,
                                      const std::string& name ) override;
+};
+
+
+class PCB_EXPR_CONTEXT : public LIBEVAL::CONTEXT
+{
+public:
+    PCB_EXPR_CONTEXT()
+    {
+        m_items[0] = nullptr;
+        m_items[1] = nullptr;
+    }
 
     void SetItems( BOARD_ITEM* a, BOARD_ITEM* b = nullptr )
     {
@@ -91,9 +96,9 @@ public:
         m_matchingTypes[type_hash] = prop;
     }
 
-    virtual LIBEVAL::VALUE GetValue( LIBEVAL::UCODE* aUcode ) override;
+    virtual LIBEVAL::VALUE GetValue( LIBEVAL::CONTEXT* aCtx ) override;
 
-    BOARD_ITEM* GetObject( LIBEVAL::UCODE* aUcode ) const;
+    BOARD_ITEM* GetObject( LIBEVAL::CONTEXT* aCtx ) const;
 
 private:
     std::unordered_map<TYPE_ID, PROPERTY_BASE*> m_matchingTypes;
diff --git a/qa/drc_proto/drc_rule.cpp b/qa/drc_proto/drc_rule.cpp
index 9611784217..51a9938f47 100644
--- a/qa/drc_proto/drc_rule.cpp
+++ b/qa/drc_proto/drc_rule.cpp
@@ -56,9 +56,10 @@ bool test::DRC_RULE_CONDITION::EvaluateFor( const BOARD_ITEM* aItemA, const BOAR
     BOARD_ITEM* a = const_cast<BOARD_ITEM*>( aItemA );
     BOARD_ITEM* b = aItemB ? const_cast<BOARD_ITEM*>( aItemB ) : DELETED_BOARD_ITEM::GetInstance();
 
-    m_ucode->SetItems( a, b );
+    PCB_EXPR_CONTEXT ctx;
+    ctx.SetItems( a, b );
 
-    return m_ucode->Run()->AsDouble() != 0.0;
+    return m_ucode->Run( &ctx )->AsDouble() != 0.0;
 }