git-gui Ctrl-U (unstage) broken

Using the git-gui available with the default Ubuntu 10.10 repos, I'm
not able to unstage files with the default keyboard shortcut. To
reproduce:
1. Change a file in the repository
2. Run `git gui`
3. Stage the changed file
4. Select the changed file in the "Staged Changes (Will Commit)" list
5. Click Ctrl-U

Expected outcome: The selected file should be unstaged.

Actual outcome: Nothing at all changes in the GUI.

Verified that other keyboard shortcuts work: Ctrl-T, Ctrl-I, Ctrl--,
Ctrl-+, F5. These (except Ctrl-T, obviously) were tested in* both the
"Unstaged Changes" and "Staged Changes (Will Commit)" listsp

* That is, after focusing a single element in that list.

Version info:

git-gui version 0.12.0.64.g89d6
git version 1.7.1

Tcl/Tk version 8.5.8
Aspell 0.60.6, en_US

Cheers,
V