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Some time ago I noticed a strange behaviour on my computer running Ubuntu 12.04.

Here's a detailed description of the problem: I log into my account, work for some time, and then somebody else wants to use the computer so I switch users to the guest session. After some time I get back and also switch back to my account (without logout/login all the time).

Now my display always freezes upon actions with the Unity desktop. If I select an Application or scroll through the sidebar or even if I start a program and a window is created. Everytime my computer freezes for about ~10sec before continuing.

Also there are strange artefacts appearing (yellow or green blinking fields sidebar descriptions) and if I scroll through a page in firefox the upper "taskbar" is somehow "mirrored" into the page (but upside down).

I usually then have to restart lightdm to fix this problem, but it's a bit annoying to always restart lightdm.

How can I fix this behaviour? Thank you very much !

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by the way, I addtionally already tried to reset unity, which seems to solve the problem until switching again. Which makes it much more likely that the problem is caused by Unity. –  ch.bailey Mar 16 '13 at 17:24
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are you completely logging out of guest session after they are done or just switching users again. I had the same problem not logging out of the guest user before switching users. You may be able to right a script the automatically refresh unity on start/log in.

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I am switching users, so I don't logout completely. But as this behaviour does not only occur on guest sessions but also on other users it is a bit uncomfortable to always logout if there's unsaved work. - But I will check if the problem occurs on a complete logout. –  ch.bailey Mar 17 '13 at 13:50
    
So, I just checked if it also happens on a logout of the guest user and I can confirm the problem there. So it doesn't matter if I just switch users or logout of the guest session. But logging out myself completely and logging in again returns the desktop to normal behaviour. –  ch.bailey Mar 17 '13 at 13:54
    
I tried reproducing this issue on my 12.04 ubuntu box and cannot reproduce the issue. This leads me to believe that it is an issue caused by something else. You using unity 2d or 3d? Graphics card updated or using compwiz on top of unity? Maybe a theme app of some sort? –  skittishtrigger Mar 19 '13 at 13:51
    
Unity 3D is used, my GFX-card uses the "current" drivers installed through the "Ubuntu Additional Drivers"-Application. Besides I'm using the complete standard unity desktop without any additional modifcations/themes. As described above a reset of Unity has helped, but after another logout the problem occurs again. –  ch.bailey Mar 20 '13 at 9:18
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