Race Disguise

[Gazfrost]

From Arelith Wiki

Disguise Race

-disguise_race (OR -disguise_r) allows you to disguise your race as a similar one when covered (Shield Dwarf -> Gold Dwarf, Drow -> Sun Elf, etc.), breaking the cover without breaking the disguise will not reveal your real race.

It seems this does not work for Subraces such as Hobgoblin and Yuan'ti.

[Shadowy Reality]

Those aren't subraces. A hobgoblin is not a subrace of half-elf, so that's probably why.

[Sincra]

This is correct.

Please refer to:
http://wiki.nwnarelith.com/Fully_Covered#Disguise_Race
The table here.

If Yuan'ti as a human form cannot please instead make a bug report.