I had a world running on 14w07a, and when I started the new 14w10b jar up, all my whitelists, op lists, etc. converted fine, but when I went to log on, I found myself at the world spawn point with a completely empty inventory, as well as zeroed out statistics.

Note: I did try to search for this before reporting. If this is a duplicate, it is likely because the original reporter worded it different than the few ways that I tried my search.

Edit: Found original report. I don't think I have permission to mark bugs reported by me as duplicates, which is fine. Original report is MC-50288.