If you have recently upgraded to Thunderbird 5 and are running UIS2 skins you may encounter some repainting issues with it and WindowBlinds when on Windows Vista SP2 / 7. If so you can resolve this by adding the following to the wbperapp.ini file that is in the skins directory. (Shared Documents\Stardock\WindowBlinds)
Direct2DWorkaround = 1
IgnoreApp = 0
Save the file and then close and reopen thunderbird and all should be fine. If this file does not exist then you should create it.
We will release an update with this added to the internal WB list but until then the above will achieve the same result.