It's just the charts, if your miner is mining, the shares are being mined and your payment will not be affected.
I've never found this to be true in about a month on Middlecoin. Whenever the stats flatline, my payouts are considerably down for the day. Disclaimer for the fanboys: not saying there's anything untoward going on with H20, nor that it's not all worth it since *on average* payouts are still better than the competition. The guy's a hero with coin trades, but there's no denying that he does a terrible job with server maintenance, and it *does* affect payouts.
Still, you don't see me leaving, yet. Cost of doing business, and all that...