I am giving my follower armor pieces to put on and I can see my follower put on each piece while in HUD. When I exit HUD my follower takes one of the pieces off. This happens even if there is nothing in the followers inventory but the one armor piece. What might cause this to happen?

Can you equip the armor on your character?

It's possible the armor isn't partitioned correctly to the right body slots, or several pieces are using the same body slots, causing the one piece to be removed.

I just want to know if that could happen for races with a tail slot.

Yes my character can wear the armor fine. The npc will remove the one armor piece even if it is the only thing in their inventory. Is a set of armor and the rest of the pieces work fine. The npc I am trying to get to wear it does have a tail, though so does my playing character. I will have to pick up a tailless companion and see if the result is the same.

This is a shot in the dark... but, is the one armor different type than the others? Like is it heavy but the others are light? If so try raising the armor skill of the follower. Especially if it has a very low skill; the hard coded AI may decide it is not worth wearing.

I am so disappointed in the lack of access to mod combat in Skyrim (the combat is more hardcoded than any of their previous games).

PLEASE Beth, change this in the next TES.

Is not a skill issue ,tested that out. Tried on a new follower and the follower wore the armor so the not wearing part is likely something to do with the custom followers design. However I got a different issue with the new vanilla follower. When I took the armor away from the follower she still appears as wearing both the armor I took away and the armor she has. Do not have these troubles on my player character. Perhaps also this was not the simple port it appeared to be. Tried porting the RRAlice armor mod by updating the nifs and deleting a cell change, but.......