The coordinates are skewed beyond -1 on the x and z axis. This affects every coordinate beyond this. Try teleporting to -1, (any height), -1. You will end up at -2, (any height), -2. It is slightly confusing, but try it and you'll see what I mean.
Environment
Mac OS X 10.8.5, Java Runtime SE
Duplicate of MC-4794 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.