Comment 2 for bug 1345771

Just wanted to report I had this same issue. It causes a major headache after switching from an ATI card to an Nvidia card. It seemed to result in a lot of black boxes popping up all over the screen. Wasn't even sure it was Compiz but when I went in and started resetting all settings to 'default' I noticed it switched from 50hz to 60hz and the artifacts immediately stopped.

Ubuntu 14.04 LTS x64
New Card: GeForce GTX 750 Ti/PCIe/SSE2
Nvidia driver 346.96