Isn't that true for all correct implementations of negative zero? It's still a neutral for addition
>>> 0.0+0.0
0.0
>>> 0.0+(-0.0)
0.0
>>> (-0.0)+0.0
0.0
>>> (-0.0)+(-0.0)
-0.0Hmm? Your examples show -0.0 being additively neutral in every case. +0.0 is the one that behaves weirdly.