Every block we mine you should be able to pay for as you get rewards so just misunderstood how you can run out of coins?
It is because this pool is with EXCHANGE of coins. What will happens if someone will mine other coins with exchange to CYR and noone will mine CYR with exchange to other coins ? The pool became debtor. He will owe more CYR's that really were mined. And will warn "We are short of this currency".
Really if you (or someone else) will mine with exchange to some shitcoin noone want to mine with exchange to something else then you will have to mine this shitcoin with exchange yourself to correct obtained misbalanse or you will get nothing. Or wait then rotating of mined coins for those who do not use -mc option will slowly correct misbalance.