Question: What happens when a transaction is included in more than one block?
Don't break the forum rules,and no PLAGIARIZING!
Only one transaction will be considered valid (the one which gets included in the block that is broadcasted first on the network). The other transaction (and/or block) will be considered invalid and will be rejected by the nodes.
Source:
https://bitcointalk.org/index.php?topic=216938.0