I have heard before that bids can be put in without sufficient funds in the account
I'm not sure if those orders appeared in the order book or if it was something account internal, but I think you refer to this:
I was actually referring to comments about lag being caused by the trading engine having to check funds. I don't know at which stage of the process this was occurring and am not trying to spread any FUD. It was discussed here and someone probably knows the answer better than me