Armin: that's a separate issue, and is expected behaviour.
>>> -(0j) # this is -(0+0j)
(-0-0j)
Yes: 0j is complex(0.0, 0.0); negating negates both the real and imaginary parts.
>>> (-0-0j) # but this equals to the difference between 0 and 0+0j
0j
This is an operation between an integer (note that the initial negation is a no-op) and a complex. Here the integer gets promoted to complex(0.0, 0.0), and we do complex(0.0, 0.0) - complex(0.0, 0.0), which gives complex(0.0, 0.0).
>>> (-0.0-0j) # this is the difference between -0.0 and 0+0j
(-0+0j)
This is complex(-0.0, 0.0) - complex(0.0, 0.0). The real and imaginary parts are operated on separately, and in keeping with IEEE 754, the real part is evaluated as -0.0 - 0.0, which is -0.0.
>>> -0j
-0j # <- on CPython 2.7
(-0-0j) # <- on CPython 3.5
The Python 3 behaviour here is correct. The Python 2 behaviour is the result of an unfortunate AST optimization designed to ensure that -<sys.maxint+1> is an int rather than a long.
None of the above is a new issue.