[Vimperator] undo close tab question

[guivho]

Undo close  doesn't seem to work for me (neither the simple 'u' nor the
':u' version). From time to time, I am a bit too fast in 'd'-eleting a
tab, and want to get it back. I assume 'u' or ':u' should do the trick,
but it doesn't. As a matter of fact, ':undoa' doesn't do anything
either. This might very well be due to minefield (=firefox beta 3)
rather than vimperator, but I'd like to know a bit more about it.

:version
Vimperator 0.6pre (created: 2008/01/23 19:02:56) running on:
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9b3pre) Gecko/2008011504
Minefield/3.0b3pre

TIA, Guido