To be clear, I agree -0.0 is "the correct" answer, and -1.0 is at best defensible via a mostly-inappropriate limit argument.  But in Py3 floor division of floats returns an integer, and there is no integer -0.  Nor, God willing, will there ever be ;-)

Looks to me like what (Py3's, at least) floatobject.c's floor_divmod() returns (the source of float floor division's result) when the 2nd argument is infinite is largely an accident, depending on what the platform C fmod() and floor() happen to return.  So it would require special-casing an infinite denominator in that function to force any specific cross-platform result.