I don't know how to find the earlier discussions of the problem, that unrelated sites seem to hold copies of MO (and/or of other SE sites) [I searched meta.mo with keywords "clone", "copy" "piracy"... but those keywords didn't help] but I think I remember a remark anywhere that such cases should be reported.
When I tried the google search for "zeta isogone" (to see how google positions its findings - inspired by the other discussion on meta) I find
http://newtips.co/mathoverflow/questions/221202/how-to-formalize-the-loci-of-equal-arg-zetas-isogones-in-the-near-of.html
(I removed some google-specific content in that link, I hope it works anyway)
Ah, and I don't find a good tag for tagging this correctly, sorry, perhaps someone might help here