Can't see drop-down menus since last upgrade

[qianian]

Since the latest upgrades for Precise 12.04 drop-down menus show up on the bottom layer, behind any open windows. I can only see them if windows are minimized and the menu drops down from the top nav bar.

Any way to control this?

[qianian]

Solved after reboot.

[Xupz]

This has been happening regularly and very randomly on my desktop for a while now. Rebooting does fix the problem temporarily but is there no other solution? Because this is getting extremely tedious.