When I enable visual effects (compiz) in ubuntu and enable seamless mode, the window borders and title bars disappear from the linux windows. If I drag a linux window on top of another one, it becomes visible again.
In normal windowed or full screen mode everything works.
If I disable the effects it all works fine, but then the windows don't have 3d acceleration and everything is too choppy. I tried disabling only certain compiz effects but none solved the issue.

Should I report this as a bug? Anyone else has this problem?
If you have any ideas about what is causing this please share it, thanks!
Btw, I'm using latest version of everything, ati drivers, virtualbox, untunu, guest additions, windows, I have an ATI Radeon HD 4850 and AMD Athlon II X2 250 3.0 Ghz, and both windwos and ubuntu are 64 bit.