My guess would be that the Mhash/s* is adjusting since it's on to a new block. That hash rate number is based on "shares so far" on the current block so the bigger rigs probably take over a little faster and then it smooths out as time goes on. Just my theory. I guess it would only be problematic in really fast solved blocks? But I don't think your equipment has any issues if it comes back over a short time.
Thanks for the reply -
I may not have explained as well as I could have. It doesn't seem to me to be a short time (relatively speaking I guess) and not just in blocks that are solved quickly. I usually am running between 96 and 101 Gh/s and my miners are steady within that range until a block is found. Once a block is found and the stat page has the block in 'processing', I am hashing between 85 and 89 Gh/s for the 35 - 40 minutes (or so) it takes to finish processing. I watch for a recovery to the 96 to 101 Gh/s rate and it only comes back after I have a reward posted and 'processing' is no longer displayed for the block. This has happened 7 times in a row that I have made sure to watch. I was going to wait for the current block to finish before posting, but its taking forever

I originally thought it might be adjustment to the new block...and I guess it is still possible, but it just seemed odd that the hash rate dropped right when the block was found and processing started, then came back when processing was finished for every block I watched, no matter the speed of the block. I guess I will make some more observations that are better timed to see if I find more clues.
Thanks again...