This is on Mac OS X 10.5
I recently changed from a German to a US keyboard where the Y and the Z key are swapped. So now I still sometimes press Y instead of Z to zoom in Preview.
This of course makes the "copy files" dialog pop up. If I want to close it by pressing esc both the dialog as well as the Preview window close.
But now PM hangs. If I click into the Contact Sheet I just get a warning tone like there was another window open that blocks action in the Contact Sheet window. But there is none.
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Cheers!
Thomas