MtGox is the only one using the TXID hash to track unconfirmed transactions. The problem with the other wallets is that if you try and spend a change address from a rewritten transaction before it is confirmed then that transaction involving the change is then invalid.

Edit: Here is a good explanation of what this latest problem is which is different than the problem MtGox is struggling with http://www.reddit.com/r/Bitcoin/comments/1xm49o/due_to_activ...