'Alt' key strange behaviour in gnome/metacity

["Antonio-M. Corbi Bellot" <acorbi@dlsi.ua.es>]

Does any one use gnome-2.6 + metacity (2.8.1-3)  and has observed a
strange behaviour in the Alt key when typing, i.e., Alt+Tab to change
focus between windows?

After upgrading to the latest xfree (4.3.0.dfsg.1-5) in SID the Alt key
seems to get 'pressed' some how and after releasing it I have to press
it again to 'unpress' it (as a side effect, the focus in windows doesn't
change).

If I change the WM without leaving the gnome-session, I've tried with
xfwm4, it works well, so it seems a metacity problem...but I did not
observed it with 4.3.0.dfsg.1-4

I also work with an x86 box (debian testing) with metacity 2.8.1-3 and
xfree 4.3.0.dfsg.1-4 and it does not have this problem.

Any ideas?
Thank you.