There was a major blockchain fork in one of the coins that we were mining. Several mined blocks were orphaned and the stats were automatically updated to reflect this. This is why there are statuses like immature and unexchanged - because value of these coins can change or even amount of these coins can change (in case of a fork). Only payable balance is a solid, final number. All auto-exchange pools work this way.

Because of this fork, Cryptsy halted all deposits for this coin and we were waiting almost five days for our deposits from this time to be credited. We are still missing one deposit worth ~0.67 BTC and I have a ticket opened at Cryptsy with this issue. I expect them to solve it today as there are no current problems with this coin. Most likely these are the coins that you have in your unexchanged balance, if you say that you haven't been mining since Feb 10th.

If you're asking why your last payout was 2 days ago, it's because you don't have enough payable balance for a daily payout, which is minimum 0.01 BTC. There is also a weekly payout for all balances above 0.001 and it runs on Sundays.