Shares accepted vs hash rates?
The pool might be adjusting your share difficulty level. For example, you might be mining at 50 KH/s and the pool is setting your share difficulty at 16. If you then increase your hashrate to 100 KH/s and the pool changes your share difficulty to 64, then you will submit shares half as fast, but receive four times as much credit for a share at difficulty 64 as a share at difficulty 16. Ultimately, you get paid twice as much mining at 100 KH/s as at KH/s, so don't worry about it.