I believe it was a mistake like you say, it would be pretty bold for an operation as large as CEX.io to think they could hide 2 found blocks worth 25,000.
well it took me a total of 3 minutes to confirm and find the blocks that were processed, and compare the results to my paid blocks and see I was not paid, but it has been well over 9 hours and we still have not been rewarded. So i guess they are taking the "bold" approach here.
EDIT: they have paid for the two blocks, Luckily I made a profit since they were mined with the cloud and have recently been incurring HUGE maintenance fees. PHEW