When you press F3 and go to 0.0 rotation, it says -0.0, which does not exist as a number.
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if you issue /tp @p ~ ~ ~ 0 0 it's displayed as (0.0 / 0.0 (correct),
if you issue /tp @p ~ ~ ~ 0 -0.02 it's displayed as (0.0 / -0.0) (still correct),
if you issue /tp @p ~ ~ ~ 0 -0.05 it's displayed as (0.0 / -0.1) (still correct)
See http://en.wikipedia.org/wiki/Rounding
-0.01 exists well as a number.