I am not sure if this answers your question about the stuck balance. But could it be that the coins that need to be traded into btc are off too low of value to be traded at any exchange. For example cryptsy wont let you trade 1 dvc since its its value is too low for a trade so you need a couple of coins. Since these are pools that mine multiple coins maybe the last of these get get stuck. I had the same problem when I stopped mining. I do mine it as my backup pool now with a couple of old usb dual miner sticks running on cleaver as primary.