Thanks for reporting.
This sounds worrying.
However, I cannot reproduce the problem and there is nothing in the latest update (from 0.5.1-beta to 0.5.2-beta) that has to do with balance checks. Moreover, if you were to get any error message on order placement, the whole DB transaction would roll back and no order would be placed. So something is very strange here.
Could you please guide me so I can reproduce your steps? It’s best if I use the exact numbers that you used to test. Also, can you check your transactions in the admin screens to verify that the order was executed?
thank you