Mercenary: Fallen Reverend's Reinforce ability - bug or intended?

I noticed that the Fallen Reverend's Reinforce summons (Osseotitan, Bishop, Emperor) just generally stay in the location where they were summoned in the map (they don't follow you around like the spectres). I don't know whether this is because they move too slow and therefore just get left behind, but they also don't disappear and the Fallen Reverend does not resummon them in the same map. Once they get summoned they just hang out in the same area and so are pretty useless the rest of the time. Is this intended?