Such things are standard across all brokers.
I don't know of any other exchange that does this. If they did truncate values then I wouldn't be using them anyway and I'm pretty sure other traders wouldn't either. I recall the huge outcry back when Tradehill started and people heard they use "float" datatypes to calculate trades.
I'm pretty sure that the remaining 0.009 BTC is not in my account. There is no indication of it.
I'd be happy to close it and have it sent out though if that were even an option.
But the main point is that none of this is disclosed up front and when I decided to send my NMC there to trade I saw no indication I'd end up paying 20% fees for the transaction. The first I saw of this was that my NMC balance was truncated and by then it was too late to do anything at all.
At the very, very least if the extra BTC portions are actually still on account then that needs to be displayed as otherwise there is no way to enter orders and do trades that make use of the balance remaining, and it may just as well be lost. The whole thing seems ludicrous and poorly conceived.
Maybe it's just inept design, or maybe it was purposefully done to grab fractional trade fees. I'm just alerting users so they know before they send funds into this leaky account.
Furthermore BTC are always calculated with 8 digits precision. Some day when 1 BTC = 100USD this truncation will be costing dollars per trade. Maybe you're used to USD where the normal precision is 2 digits.