Hi Guillaume;
Yes,I have seen this behaviour as well the odd time. Its normally not a problem for the application user if they can just drag their application window a little higher. BTW: I can get the same issue with IE or Firefox on various web applications that do this as well.
Suggestion: An easy fix for the application user for PB and other various applications that can be affected like this is to ask the user to set the task-bar into "auto-hide" mode. This easy change seems to alleviate the issue for my clients .....
Regards ... Chris