Ah, I think this is the same problem that the author of the FB data files reported to us a while back. Unfortunately we didn't have time to implement a fix in AB3.3.
If you mark the Fire Dragon Exarch as "effective", the minimum limit will work properly. Unfortunately you'll then have the opposite problem - the maximum limit will be 1 too low with the Exarch added. The FB data files solved this by making the upper limit for the unit 1 too high, then giving a validation error if you took the maximum number of guys.
Unfortunately I can't think of a better way to handle this right now.
It is on our to-do list, and it's hopefully something we can tackle in a future release of AB.