I originally reported this as a comment to MC-56310 on August 5, 2014. MC-56310 was resolved as "downgrades not supported". I understand this from the perspective of a bug against 14w31a but after further reflection I decided that a much more appropriate place to enter this issue report is against the launcher itself. For it is the launcher, not the Minecraft snapshot, that allowed for the deletion of all my inventory, out of all chests, etc.

I had this happen to me today with a world originally created with 14w31a (the lastest as of today). I accidentally re-entered this world after changing my profile to 1.74 Vanilla. The result was that my built world was intact but all inventory items from my person and all chests throughout my world were empty.

I reset my profile to 14w31a and re-entered my world again. All my inventory was still empty. Luckily I had saved a backup from earlier that day so I was able to recover somewhat.

The Minecraft launcher allows for multiple profiles for a given user, each with the option to set the Minecraft version. What I did was an accident but an accident that I believe will happen a lot in the future.

I entered a 14w31a world under a 1.74 vanilla profile and the Minecraft Launcher gave absolutely no warning that my versions didn't match. This alone should be considered a bug, in my opinion. Had I been issued a warning I would have immediately remembered that I needed to change my profile back to 14w31a.

Since different Minecraft versions are supported by the Launcher it seems to me that proper care should be made by the Launcher when catastrophic changes can be made by entering a world under the wrong version.

Of course the user should still be given a choice to proceed or not so all I am really asking for is a warning message and a prompt to continue or not.

Bob