WPF Application takes too much CPU for some users
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I have a WPF application written in VS2010 Express for .Net 4. Some testers report that the application takes alot of CPU (~80%-100%) whenever the application window is visible and 0% when not visible. This is not the case on my computer, nor on the other computers i have tested. What I see is that it takes a bunch of CPU for the first few seconds after opening the window, but then goes down to a few percent.

My suspicion is that this is an issue with the rendering of the WPF window. But i can not understand why it only occurs for some users. 

I understand that this is not much to go on, but if anyone have an idea where to start looking for the cause of this performance issue, it would be much appreciated.  

Thank you!