I had the following issue when I promoted a Horse Archer to Mobility (via Flanking I and II). When I mouse of the the promotion it said something like:
+124419 movement cost
I was expecting it to read like it does on the fold out poster:
-1 terrain movement cost
As far as I could tell, the unit was functioning fine, so the bug was display only.
FYI, tip to those who are inclined to get Mobility...this only reduces the cost of moving into a hill, forest, etc. It does not grant you any extra movement rate. I was confused at first cause my horse archer was still only going 2 squares a turn.

+124419 movement cost
I was expecting it to read like it does on the fold out poster:
-1 terrain movement cost
As far as I could tell, the unit was functioning fine, so the bug was display only.
FYI, tip to those who are inclined to get Mobility...this only reduces the cost of moving into a hill, forest, etc. It does not grant you any extra movement rate. I was confused at first cause my horse archer was still only going 2 squares a turn.
