I have noticed that since around the time the total average hash rate changed to the last 60 minutes, the shares per worker display has become erratic. It used to show any change at each page refresh, and the number of shares always increased steadily until a round ended; now the number updates only after an interval (I have not yet determined how long) and the number of shares sometimes falls: for instance, just now when I refreshed the page one of my workers fell from 1933 to 1931 shares. Some minutes earlier it had dropped from 2053 (and now I see it has fallen again to 1905). The round and block number (299880) had not changed, the Mhash/s for each worker is within the expected range, and the time since the last share is usually zero. The estimated reward also fluctuates wildly: while I have been writing this it has varied between .00002876 and .00007421.
Could this be anything to do with the high variance in payments per round that I am experiencing? Has anyone else seen similar behaviour?

I dunno something odd always goes on with Slush Pool....
I periodically see my miners showing their hashrate 10% lower than their true hashrate.
My miners do not fluctuate below 200 mh/s so there is absolutely no reason why an hour would show 10% less.
some sit at 210 some sit at 202. so the average should always be 206ish. not 195 once in awhile.
in all reality it doesnt matter, maybe someone is skimming, maybe there was network issues (which is bs cuz that would clear up after 1 hour), there are much better things to worry about. the block ends and it goes back to normal.
I could complain and whine and maybe it will get tracked down and fixed but most likely not.
Guys, your reported hash rate on the pool webpage is just a close estimate. Go by what your mining software reports and not what the pool reports. If you really want to know exactly how much BTC per GH/s you are making, I would suggest breaking out a calculator and comparing your payouts to the blockchain and pool hash rate vs. net hash rate.
The way I look at mining...if my miners are working properly and the pool is up and reporting....so long as my payouts keep coming, I will keep mining. Go mine with another pool for a few days...chances are, you will come back to Slush pool within a week. Other pools offer merged mining and no registration and other gimmicks to entice miners but I feel the Slush pool is straight forward and one of the best share payout systems I have experienced.