Here's what happened:
I received a transfer ID before I hit the submit button. When I did, I got a red error message saying: "Limit reached or not enough bitcoins in your account." Non-the-less the entire amount (around 50BTC) did to to my working blockchain.info wallet.
...
I would have thought that Mt. Gox would have some of these UI bugs by this time which is what this looks like to me. Oh well.
You were not supposed to click on the Submit button as you had already withdrawn your coins. They should change the UI to not display the button after the screen refresh.
Ah! I suppose I had hit the enter key and that had the same effect as the submit button. I was scratching my head a bit on how the transaction ID showed up prior to submitting the transfer and thought it must be a part of an internal hot-wallet transfer or something. But I didn't think that much about it. blockchain.info beeped about 0.25 seconds after I hit the submit button. I guess that was just happenstance but it threw me off as it seemed related due to the timing.
I'd say that not only should the button go away, but the text associated with an error of transferring 0.0 BTC to a null address should be different. Neither potential problem given in the error message is appropriate for this issue.