The hero talents that a person does not have active (ie: their other hero talent specialization) appear in the list of selected_spec_talents on the api. This bug is mirrored by the armory.
For example: [armory link]/en-us/character/us/proudmoore/tekawar
This warrior is in the Mountain Thane hero talent spec but under Fury specialization talents “Slayer’s Dominance” is listed. This is not correct.