Glitches with gnome-shell 3.8 and nouveau driver?

[shuihuzhuan at free.fr]

Hello,

Yesterday, I've switched my main desktop (64 bits) to gnome-shell 3.8 with gnome3-ppa and now I've noticed some strange glitches that I don't have on my laptop with a similar software configuration (but different hardware and 32 bits).

I have an old nvidia 7600GT graphic card and I'm using nouveau as a driver on this desktop (because the proprietary driver was buggy when switching users with gnome-shell 3.2). nouveau is rather slow but it works fine.

Everything seems fine, except the rendering of some "system" dialogs. For example, when I choose "Shutdown" a system dialog opens to confirm. But when I move the mouse the first time over a button of that dialog (and only the first time), the button disappears and a bad looking rectangle appears instead. Then I move the mouse outside the button, it reappears and the problem never comes back on that button. But if I move the mouse on other buttons of the same dialog, there's the same behaviour.

I've never met such behaviour with all previous gnome-shell versions. I don't have rendering problems with panel/menus/overview/applications... just on those dialog's buttons. I don't know what has changed between 3.6 and 3.8 for such strange thing to appear. It may be related to nouveau or clutter/mutter or rather gnome-shell. But why only on those buttons? 

So while I'll try to investigate further and probably open a bug report, I'd like to know if anyone using nouveau has ever seen a similar problem (Googling around, I've not found any)?

Thanks for your advices.