Can anyone remember any loop when the price went up really fast?
If this really is a security measure it only needs to be on the down-side since BTC withdrawals are instantaneous and irreversible while fiat withdrawals take at least a day (time for Mark to wake up and notice) and can sometimes be clawed back. Blocking all BTC withdrawals from all accounts is an alternative, but that REALLY freaks people out, so I can understand why he'd be reluctant to do that.
I still think that "looping" instead of halting is completely bonkers.
While I agree with what you say, I should point out that mtgox BTC withdraws are not instant...
It takes days sometimes (longer than fiat transfers typically take).