Another newbie, thumb twiddling till his online time ticks over to 'not-newbie'.

So this should be posted elsewhere, but what the hell, don't blame me.

Quoting from http://forum.bitcoin.org/index.php?topic=7269.0[/url
New to BitCoin? Start here!

"In conclusion:  All this mathematical technology may be a bit of a mouthful, but what it means in practice is that BitCoin works just like cash.  Bitcoin transactions are intentionally irreversible--unlike credit cards or PayPal where chargebacks  can invalidate a payment that has already been made.  And there are no middlemen.  Transactions are completed directly between the sender and the receiver via the peer to peer network."

Well apparently that is all flat out untrue. If MtGox can 'roll back' a series of transactions they don't like, then clearly Bitcoin transactions ARE reversible. Which also means Bitcoins do not 'work just like cash'. Also that MtGox ARE acting as a middleman, with all that implies.
The reasons MtGox decided to rollback are irrelevant. Sure, they were hacked and 500K bitcoins sold into the market by someone who didn't own them. Doesn't make any difference, MtGox is still doing something that was supposed to be impossible, and so one has to wonder. What _else_ is untrue in the theory of Bitcoin?