Have you tried setting "Minimum difficulty" for your worker to 512? Some people reported that it helped if the miner did not switch difficulties.
Speaking of which is there some sort of tuning guide for the new options and/or bfgminer on bitminter, or is it all buried in this monster somewhere?
I wrote a bit about work submits per minute here:
https://bitcointalk.org/index.php?topic=27062.msg3142713#msg3142713The minimum difficulty option was added after that. Many suggest to set it to your hashrate in gigahashes divided by 1.4. The server will still auto adjust your difficulty, but the minimum diff gives a smoother start when you connect to the pool, so that the server doesn't have to bring you up from difficulty 1.