diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb728866a..cabdd8a34 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## 1.6.0 (unreleased)
 
+BACKWARDS INCOMPATIBILITIES:
+
+  - providers/virtualbox: Shared folders backed by VirtualBox are now
+      "transient". They will be removed if you reboot outside of Vagrant.
+      Always use `vagrant reload`.
+
 FEATURES:
 
   - **New guest: Windows**. Vagrant now fully supports Windows as a guest
@@ -37,6 +43,11 @@ BUG FIXES:
 
 PLUGIN AUTHOR CHANGES:
 
+  - core: The "Call" middleware now merges the resulting middlewaer stack
+      into the current stack, rather than running it as a separate stack.
+      The result is that ordering is preserved.
+  - core: The "Message" middleware now takes a "post" option that will
+      output the message on the return-side of the middleware stack.
   - New host capability: "rdp\_client". This capability gets the RDP connection
       info and must launch the RDP client on the system.
   - provider: Providers can now specify that boxes are optional. This lets
@@ -45,11 +56,8 @@ PLUGIN AUTHOR CHANGES:
   - provider: A new class-level `usable?` method can be implemented on the
       provider implementation. This returns or raises an error when the
       provider is not usable (i.e. VirtualBox isn't installed for VirtualBox)
-  - core: The "Call" middleware now merges the resulting middlewaer stack
-      into the current stack, rather than running it as a separate stack.
-      The result is that ordering is preserved.
-  - core: The "Message" middleware now takes a "post" option that will
-      output the message on the return-side of the middleware stack.
+  - synced\_folders: New "disable" method for removing synced folders from
+      a running machine.
 
 ## 1.5.4 (April 21, 2014)
 
diff --git a/lib/vagrant/plugin/v2/synced_folder.rb b/lib/vagrant/plugin/v2/synced_folder.rb
index cffd25626..9747b9cc3 100644
--- a/lib/vagrant/plugin/v2/synced_folder.rb
+++ b/lib/vagrant/plugin/v2/synced_folder.rb
@@ -14,21 +14,36 @@ module Vagrant
         def usable?(machine, raise_error=false)
         end
 
-        # This is called before the machine is booted, allowing the
-        # implementation to make any machine modifications or perhaps
-        # verifications.
+        # DEPRECATED: This will be removed.
         #
-        # No return value.
+        # @deprecated
         def prepare(machine, folders, opts)
         end
 
         # This is called after the machine is booted and after networks
         # are setup.
         #
+        # This might be called with new folders while the machine is running.
+        # If so, then this should add only those folders without removing
+        # any existing ones.
+        #
         # No return value.
         def enable(machine, folders, opts)
         end
 
+        # This is called to remove the synced folders from a running
+        # machine.
+        #
+        # This is not guaranteed to be called, but this should be implemented
+        # by every synced folder implementation.
+        #
+        # @param [Machine] machine The machine to modify.
+        # @param [Hash] folders The folders to remove. This will not contain
+        #   any folders that should remain.
+        # @param [Hash] opts Any options for the synced folders.
+        def disable(machine, folders, opts)
+        end
+
         # This is called after destroying the machine during a
         # `vagrant destroy` and also prior to syncing folders during
         # a `vagrant up`.
diff --git a/plugins/providers/virtualbox/synced_folder.rb b/plugins/providers/virtualbox/synced_folder.rb
index aa35b280f..1511a74d9 100644
--- a/plugins/providers/virtualbox/synced_folder.rb
+++ b/plugins/providers/virtualbox/synced_folder.rb
@@ -9,7 +9,8 @@ module VagrantPlugins
           machine.provider_config.functional_vboxsf
       end
 
-      def prepare(machine, folders, _opts)
+      def enable(machine, folders, _opts)
+        # Export the shared folders to the VM
         defs = []
         folders.each do |id, data|
           hostpath = Vagrant::Util::Platform.cygwin_windows_path(data[:hostpath])
@@ -17,14 +18,12 @@ module VagrantPlugins
           defs << {
             name: os_friendly_id(id),
             hostpath: hostpath.to_s,
-            transient: data[:transient],
+            transient: true,
           }
         end
 
         driver(machine).share_folders(defs)
-      end
 
-      def enable(machine, folders, _opts)
         # short guestpaths first, so we don't step on ourselves
         folders = folders.sort_by do |id, data|
           if data[:guestpath]