Bug #66192 Tried to open two table editors, or at least to switch to another one.

Description:
Error encountered while trying to edit tables.

----- Developer Notes -----

MySQL Workbench CE for Windows version 5.2.41  revision 9727
Configuration Directory: C:\Users\Trent\AppData\Roaming\MySQL\Workbench
Data Directory: C:\Program Files (x86)\MySQL\MySQL Workbench 5.2 CE
Cairo Version: 1.8.8
OS: Microsoft Windows 7  Service Pack 1 (build 7601), 64-bit
CPU: 4x AMD Phenom(tm) II X4 945 Processor, 4.0 GiB RAM
Active video adapter (0): ATI Radeon HD 5700 Series
Installed video RAM: 1024 MB
Current video mode: 1920 x 1080 x 4294967296 colors
Used bit depth: 32
Driver version: 8.980.0.0
Installed display drivers: aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64.dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Current user language: English (United States)

Exception = System.InvalidCastException
Message = Unable to cast object of type 'MySQL.Forms.MenuItemImpl' to type 'MySQL.GUI.Workbench.Plugins.DockablePlugin'.
FullText = System.InvalidCastException: Unable to cast object of type 'MySQL.Forms.MenuItemImpl' to type 'MySQL.GUI.Workbench.Plugins.DockablePlugin'.
   at MySQL.GUI.Workbench.Plugins.DockablePlugin.GetFromFixedPtr(IntPtr ptr)
   at MySQL.GUI.Workbench.MainForm.ShowPlugin(IntPtr ptr)
   at MySQL.Forms.AppImpl.show_editor_wrapper(UInt32 native_handle)
   at boost.detail.function.void_function_invoker1<void (__cdecl*)(unsigned int),void,unsigned int>.invoke(function_buffer* function_ptr, UInt32 a0)
   at wb.ModelDiagramForm.handle_mouse_double_click(ModelDiagramForm* , MouseButton , Int32 , Int32 , EventState )
   at MySQL.Workbench.ModelDiagramFormWrapper.OnMouseDoubleClick(MouseEventArgs e, Int32 X, Int32 Y, Keys keystate, MouseButtons buttons)
   at MySQL.GUI.Workbench.ModelDiagramForm.CanvasPanel_MouseDoubleClick(Object sender, MouseEventArgs e)
   at System.Windows.Forms.Control.OnMouseDoubleClick(MouseEventArgs e)
   at MySQL.Utilities.WindowsCanvasViewerPanel.OnMouseDoubleClick(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

How to repeat:
Opened EER Diagram, put two tables out, double clicked on one, tried to double click on another. Program crashed...

This is a duplicate of bug #66013.