How to reproduce:

1.) $ killall Thunar      # Kill all thunar instances
2.) $ Thunar /            # Start thunar in any directory
3.) At this point your console should already give you error messages such as: 
  a.)(thunar:19026): Gtk-WARNING **: Refusing to add non-unique action 'ThunarUca::action-11' to action group 'ThunarActions' more than at least once.
  b.)(thunar:18937): Gtk-WARNING **: Refusing to add non-unique action 'Twp::setwallpaper' to action group 'thunar-standard-view-custom-actions'

4.) Navigate to any folder.
5.) Select two files.
6.) Right click and select 'Move to Trash'. A couple of errors should show up already.
7.) Open up your Trash Can preferably through the desktop.
8.) Select the two files, right click, and hit 'Restore.'
9.) Right click on a file, and then right click into empty space, and click out of the context menu. Click around randomly.
10.) Go back to the directory from which the files were deleted.
11.) Right click in to empty space, and then right click on to a file, and right click on to empty space. Click around randonly.
12.) Repeat if needed.

Results:

The Thunar window from which the files were restored into should eventually update its context menus and will appear to duplicate its custom context menus.

Screenshot #1: http://i.imgur.com/K2Ii31J.png
Screenshot #2: http://i.imgur.com/UAlsmNl.png
Screenshot of GTK logs: http://i.imgur.com/Ikse9Kl.png

Suspected cause:
Commit -- http://git.xfce.org/xfce/thunar/commit/?id=dae9c330340b7fecf0986734956b794251128831

At the moment, I will wait for the original owner to comment who is also the maintainer to come in and possibly fix this before making any modifications.