I guess it is from coins that need to be manually traded and are stuck in an exchange somewhere waiting to be paid out to clevermining and then to us in btc.
There is a similar problem happening on waffle pool at the moment, they are changing the way they pay out from once a day to multiple times a day. The opposite of what some people are asking for on clevermining, I hope if Terk changes to one payment a day we don't run into this same problem here as wafflepoll are now encountering.
Note: Payouts are being changed slighty (multiple times per day), please see here for more information.
Those of you still mining at our default domain (wafflepool.com instead of one of our geo-located hosts), please update your configuration as we will be disabling mining on the base domain in the next couple days.
Payouts (Feb 26th)
Over the past few days we have been having delays on payouts from one of our major exchanges that we trade coins on (Cryptsy). Essentially we request bitcoin withdrawals for all of the amount we have held with them (enough to cover all of our payouts), however, by the time the withdrawal clears (6-12 hour delay recently), we have accumulated enough new earnings, that we no longer have enough funds from that withdrawal to complete payouts, and have to start another withdrawal (perpetually).
Starting today (until this is fixed, or we have a better solution), we'll do rolling payouts each time one of the withdrawals clears, and will continue to pay users with the same threshold (0.01btc). We will pay groups of users at a time, and will select users on the basis who hasn't been paid in the longest time. Everyone will still be paid their full earnings, there are no coins missing, etc. We just need to start paying in smaller batches, a few times per day (instead of one large batch).
I'll try my best to get this resolved as quickly as possible so we can get to a state of consistently timed payouts, but right now, the majority of this is out of my hands, and I'm waiting on responses from Cryptsy