I thought I would just point out that after converting to a new snapshot and clicking backup and load, the original world does corrupt (as in chunks completely reset to default terrain). After trying to load the backup, the backup is corrupted in the exact same way.
EDIT: So I did a bit more investigating and it turns out that this seems to occur if command blocks are running when you load the world. The world seems to load fine as long as they aren't running.
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testing discovered 1
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I can't seem to recreate this scenario consistently. It always corrupts when going backward in versions, but it seems to be random when going forward. Whatever happened seems to have been fixed in the latest snapshot (17w49b), as I haven't had this problem with the latest one. You can mark this one as closed if you want.
Do you still want the zip file?
Nothing will ever support going backwards in versions, if you have issues going forwards from non-snapshot versions we'll look into it!
Could you attach a zipfile of the world where these problems happen?