Bitcoin spend before received When browsing the blockchain.info I came across this address. It seemed peculiar to me, that the amount of 0.6 BTCs has allegedly been spend before received. 

Is it because the "receiving transaction" somehow occurred in a side-chain and has only afterwards been merged into the Blockchain? Or what other explanations might there be for this behavior?
That's an interesting find! The transaction that created the output was in block 274227. The transaction that spent the output was 6 blocks later, 274233. So it's perfectly valid on the bitcoin network even though blockchain.info seems to have a glitch in the times they are reporting.

If they are basing the received time of the transaction at all on the time of the block it was included in, then you should know that the time recorded in bitcoin blocks can be a little off sometimes. See Why don&#39;t the timestamps in the block chain always increase?. Although, this doesn't appear to be what they are doing since they report two separate times, one for when the transaction was received and one for the time of the block.

Blockchain.info's API, Wallets, and Block Explorer are not known for being the most robust. They have started a bug bounty program, though: https://www.crowdcurity.com/blockchain-info.