I am not talking about using DK eyes, I'd rather find a way to turn off that damn failsafe and use the real npc skins without using contrived work arounds.
As for the cache, nope, this is a core issue.
Trinitycore, and probably most other cores by now, automatically translates anything not possible in retail as 00 to the player watching. Just like the OP has illustrated in those screenshots.
This is not only for Dk eyes, this is for EVERYTHING, every skin a race/class cannot normally get is blocked by the failsafe.. From Mag'har, to Cultists, to Wildhammers, to High elves, Whitemane etc.