Quote from: Stammer on February 28, 2014, 04:58:39 AM

My understanding is that indeed only one transaction gets registered in the blockchain, but there seem to be different takes on this issue.

This is incorrect. Maged is describing what happens to competent exchanges with the malleability bug in the quote -- and it seems MtGox was not one of those.

The claimed explanation for MtGox was:
* MtGox sends a transaction
* attacker modifies the txid
* modified transaction goes in the blockchain, and bitcoin ownership changes
* attacker complains MtGox "I didn't receive my coins"
* MtGox searches for original txid in blockchain, doesn't find it (<-- this is the bug)
* MtGox thinks they haven't paid, apologizes and sends a second, totally separate transaction of the same value

So there will be two transactions in the blockchain (Maged even says so in his post "Under no circumstance should you just issue a completely new transaction like MtGox did. That is how they lost some bitcoins"). Identifying the pairs could be very difficult as the sending and receiving addresses might be different.