BartPe

So, did you finally find the cause for this one? I'm seeing the same issue in our environment.

Did you look at the "point and print" GPO settings? With the Win7 GPO templates you can configure your point and print settings also on computer level ("administrative templates\printers"). I had a similar problem where my printers didn't install via login script on Win7 machines. Solved this by configuring the point and print restrictions on computer level.