Settings button on the upper right corner does not work...

[lz1dsb]

This is something I noticed recently. The settings button on the upper right corner is not working anymore. I don't get the menu I used to get. When I click on it, nithing happens. When I click on the Settings icon on the Unity panel it works.
Has anyone else experienced this?
I'm running version 12.04

[lz1dsb]

It seems like this issue disappears when I reboot. And it's there from time to time...