When the player is being relatively teleported to negative coordinates the command doesn't check for the parameters. It only happens with @a and @p not @e (or their name, but that is obvious), I am not sure if it does this for ALL kinds of parameters, but I know for sure that it does this for scoreboard parameters. Test this out by creating a scoreboard objective of, say "test", then give yourself a score of 0 "test" then type in "/tp @a[score_test_min=1] ~-1 ~ ~". If this glitch exists not only on my minecraft but on the whole snapshot, it should teleport you despite the fact that you have 0 "test".