Weird Windows aspect after gnome-shell

[frankdd89]

Hi Fedora people! My name is Francesco and i've recently installed Fedora 13 Gnome x86_64.
The installation was fine, after all the updates were done, I've installed Mesa-dri-experimental and then Gnome-shell.
After I activated Gnome-Shell windows have some weird aspect (see image below )

I've a acer 8930g laptop with a geforce 9600m gt.
Do you have any Idea of what's wrong?
I've also noticed that this problem disappear as soon I apply a theme with non rounded windows ( like Crux )

[CSchwangler]

I guess you know that Gnome shell is still under development?