That's at least partly confusion about how Special Skills work (which is a serious issue in itself). If a unit (at the unit level rather than the individual option level) has the Fireteam: Duo Special Skill, it has that Skill. Period. No matter which faction or Sectorial that unit is appearing in, in just the same way that a unit that has V: Dogged always has that Skill listed. As per the Fireteam: Duo Skill, you must check the Sectorial chart to see if a Duo can be formed in that Sectorial. The same applies to the Fireteam: Haris Special Skill, but that's more often an option-level Skill rather than a unit-level Skill, in which case the Haris options only get listed where appropriate, rather like the Sectorial-specific loadouts for Ninjas or Devas. So technically, the actual bug is that Army isn't showing Duo all the time, and (as we're all aware) doesn't list Fireteam options consistently.