I solo'd Anarume and didn't get credit for the kill... I know it was bugged before but supposedly patched in 1.5... now looks like its bugged again... XBNA
Many World Bosses can be killed outside the area where you'll get credit for the achievement. However, I've killed many of them right on top of their spawn point without credit. It happens sometimes.
It's much more irritating now that WB's are such a PITA to do, but it's a bug that's been in the game since release. Since so many people farm WBes now, I doubt ZOS considers fixing this to be much of a priority.
Edited by MasterSpatula on January 17, 2017 7:24PM
"A probable impossibility is preferable to an improbable possibility." - Aristotle