This is just poor bookeeping on Mt.Gox side.
This is exactly what it is. Poor bookkeeping, nothing more, nothing less.
Pretty clear to anybody with an average understanding of Bitcoin... But I have to say that I'm enjoying all this noobs with low activity screaming and crying about Bitcoin possibly going to 0... I bet that they are the ones who sold me all those $550 coins on Bitstamp, now hoping to grab some $450 coins.