Does the pool penalize for incorrect shares?

I ask this question because I have two cards that are producing an "incorrect" share rate that is unacceptable (15-20% of all shares appear to be invalid.)  I've attempted to correct the problem via voltages, power, reducing clocks, reducing intensity (memory usage) etc.  Nothing seems to work so it must be a problem with the card memory.  In either case, Claymore was showing a hash rate of 2830 H/s, but the pool was only showing a hash rate of 820 H/s.  That is a very large discrepancy that I haven't seen before (usually the two are very close) and trying to determine why that may be.