It's because MTGOX was told about the invalid issue back in September and did nothing about. They tried to do withdrawls last night but it failed again.
It got so bad that the CEO of MTGOX has stepped down tonight. So people are freaking out about the BTC on MTGOX.
DO NOT take MTGOX prices seriously since you cannot withdraw any of the coins from them.
http://www.cryptocoinsnews.com/2014/02/24/breaking-mark-karpeles-resigns-bitcoin-foundation/
Big news after the failed withdrawls from last night....
I think that move was to take the money and run because he has massive BTC in his stash