A negative number raised to a noninteger power will give you a complex result. This test was added from issue 2084 (https://code.google.com/p/sympy/issues/detail?id=2084), the discussion there gives the limit as `oo*E**(-I*pi**2)`; if that's right, then I guess `zoo` is ok, but `-oo` not. See also the commit  that added this test: bbe65fb34971b40b35027585fd2012cc2eb968b4.