The following zero check yields an error in my copy of Sage (version 9.5):
real_part(log(QQbar((-1)^(1/3)))).is_zero()
The result of the computation should be True. The entire error message can be found here: https://pastebin.com/iYNjuwZJ
I also checked the Sage Cell Server and the same error appears there. I could not find anything related on the Trac server. However, since I have no idea what is going wrong here, my search was very limited.
