Problems with window switching with Ubuntu 12.04 guest

[CodeInABox]

Hello!

I am having Windows XP and recently updated to the newest Oracle Virtual Box version. I installed Ubuntu 12.04 as a guest system and activated 3d acceleration for the unity surface of Ubuntu (wasn't smooth beforehand). But now switching between host and guest windows doesn't work fluently anymore. The guest window doesn't appear opaque when I switch between windows. Only the header line. I first have to invoke "full screen mode" to see it as a whole.

Moreover, copy&paste between host and guest doesn't work. it worked with the old setup (older virtual box + ubuntu 10).

Does anyone know what is causing this?

My laptop has 4 Gig Ram and I assigned 1.5 Gig to the guest.

[CodeInABox]

I unchecked 3D-acceleration and it cleared the problem. However, this affects the performance of the Unity graphical surface of the Ubuntu 12.04 installation of the guest