Double logging on the same account and starting a lan world on single player on one account, then accessing the same world in single player mode, causes the game to load save data from the last logout of the account in single player mode even though the actual last logout occured on the world opened in lan, causing any progress on the world in lan mode to be lost.
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Is this still a concern in the current Minecraft version 1.7.2 / Launcher version 1.3.4 ? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
This is not a duplicate of MC-697. This bug is not about duplicating items from one player to another; it is about a single instance maintaining two versions of a single player's status, and reverting to an earlier version.
I believe this is a dupe of the core problem behind MC-697.