Markus,
I use PI and I agree, I know I've seen that problem *somewhere* - I just can't remember where.
However, WebIS (the makers of Pocket Informant) have a great support page and should be able to answer your question quickly.
It is:
http://www.pocketinformant.com/support.php
Wait... the original problem is coming back to me now... Check the date of the task in outlook and then in PI - make sure that it's set properly... something about it being past midnight. I know that's not helpful, but it's what I remember.
Try the support forum, let us know if that helped..
Nick