Since last April I start every month at -22,5$ because of a refunded sale (a video). Since, I need to add this amount to the account stats to get the actual balance. Despite the error in the monthly balance I get the correct payout every month but it is very annoying having to add this amount every time I check my stats. BTW, I have contacted support many times since I first noticed this bug and have been told that this is not important as long as I get the correct money every month :-(
Of course this is a bug, but given the very serious bugs they are having lately, I guess they are not going to work it out, so I'm learning to live with this...