it does sometime, but at the end, the total coin will be approximately the same as expected.
I sometime during the nice hash, I switch to other coin and come back.
Well, it's been happening to me for a few days in a row, so I eventually just gave up and switched to Bitcore. Been getting more from mining BTX than from Smartcash before. I also tried mining smartcash solo, but didn't have much luck for some reason. Spent 3 or 4 days on that and got a lot less coins than I was getting from the pool before. Could've been luck, I don't know..
Same with Neoscrypt coins. When NH joins, everything gets fucked up. Not only skyrocketed diff, but also your miner starts switching between coins by itself, loosing hashrates.
That is confirmed yyimp-like pools issue, I hope it will be fixed soon