Arelith

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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.

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

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.