You could also setup advacned logging to determine if it's a bad record: BlackBerry Search Results
It can happen with any PIM item, mostly the Calendar though. How many contacts are in this Public Folder? I'd becareful if it's more than 6000, the contacts DB on the device gets slower and does not perform as it should. I think it's a limit on the DB itself even though the device memory is ok.
I was working with a guy once who had 16,000 contacts and the lookup feature didn't even work, but the contacts only used 3MB of memory.
Just something to keep in mind.