Yes, I have had this problem with several of your builds and the generic build based on Cheimisists changes (https://bitcointalk.org/index.php?topic=253662.msg2716037#msg2716037) as well, but not the release 5 build. The strange thing is that the problem doesn't occur right away, I have observed it getting stuck on the same block after working flawlessly for 7 hours. I don't end up with any orphans though, I only observe that it's working on the same (old) block for a very long time.

Would getting stuck on one block (not following the chain anymore) indicate a flaw in the build I'm using, something going wrong on my computer/connection or with Primecoin in general? This has occurred 3 times today, but not once before that. The issue happens long after I started mining, anywhere between 1 and 5 hours after startup. I have been using the following builds and had this happening with both builds:

Generic Windows client based on Chemisists improvements, compiled by fabrizziop
https://bitcointalk.org/index.php?topic=253662.msg2716037#msg2716037

Release 16 Windows client optimized for SB i5, by Zalfrin
https://bitcointalk.org/index.php?topic=253662.msg2711432#msg2711432

Primecoin being restricted to CPU mining at the moment doesn't really matter when you only pull at most 4000 PPS on a non-specialized computer, considering people have VPS clusters totaling 100k PPS. Hopefully a GPU miner will make VPS mining inefficient.