Ctrl - Z doesn't undo delete

Delete a message in Mozilla Thunderbird.
Type Ctrl-Z
The message should "Undelete" but does not.

This is not likely Thunderbird's fault, but rather likely rests with something in the Window manager or Gnome.

Similarly under Firefox the Backspace key does not give the Firefox behavior of going back one page in it's history.

The Undelete function does work from the menu.
     "File" -> "Undelete Message"

Thanks!
-Joe Baker
Ubutntu 6.10 and LTSP 5 as provided by Ubuntu - Running XDMCP instead of LDM.