C'thun, Temple of Ahn'Qiraji - Dark glare movement

[Silverfalll]

Playing on vanilla (current patch 1.9, Everlook server), doing C'thun (npc=15727).

His Dark Glare (spell=26029) makes him move erratic back and forth, instead of a clear path like intended.

Say his glare is starting at 90deg (with intended end destination 180deg):
Instead of ticking *90-95-100-105-110-115....
His glare goes 90-80-95-75-90-75-150-110... before suddenly popping to 180.

*(tic deg. for demonstrative purposes)