It could be that summoning a lot of stuff caused scrolling, and scrolling then messed up the script that reset follower position after combat. Will try to see if I can recreate it!
Fracturing a dragoon to another follower should properly give them 4 trait slots, although having 2 dragoon traits on the same follower won't stack. That's because the wording of dragoon's trait is supposed to be [4] [additional traits] rather than [4 additional] [traits]; sadly we haven't found a better wording for it yet :(