Originally Posted by
morika
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It's rare that something like releasing the wrong build for a demo or patch occurs but isn't that hard to explain. There are usually multiple builds floating around at any one time, spread across multiple platforms, it isn't so hard to believe that one of these could accidentally be mixed up with the genuine article in the rush to get it out the gates. I've seen one or two colossal mistakes happen this way, thankfully not in the public domain.
As for different versions, this happens with most games that have expansion packs released for them, and the same applies to version updates. Person A has DLC pack 1, and person B doesn't, a minor patch is all that is needed for B to connect to A. Clearly there are some compatibility issues as people have been reporting a distinct lack of lobbies for gamemodes other than Conflict. But no, it is by no means impossible to use multiple versions of the same game in the same lobby.