I think I've noticed a bug on Mt. Gox, but figured I'd post it here to see if others have seen this or if I'm just imagining things.
If you have an order that gets split because of insufficient funds, and the part that you have funds for gets executed, the other part disappears.
So, for example, lets say you have an order to sell 100 BTC @ 2.50, but you only have 50 BTC in your account. On the trades screen you'll see the order split in two - an "active" 50 BTC order and an "insufficient funds" 50 BTC order. If someone bids 2.50 and the active 50 BTC of the order is filled, the "insufficient funds" part of the order will mysteriously disappear.
Anyone else notice this behavior? I'm pretty sure I've seen it 5 or 6 times at least on my account over the past few weeks.