So wait, their "close order" button closes your position by taking the opposite position for the same amount as your open position, not based on the open order's ID?
Exactly.
Their trading engine was maybe good enough when they were a little exchange, I think they had scalability problems and it wasn't properly coded for that scale.
A trader I know got some big loss due to their incomptence, and they still refuse to give him a complete refund :
https://bitcointalk.org/index.php?topic=1165622.0