Quote Originally Posted by Ferromancer
Build a "field of games" in a Casse city. Train a unit, it gets an experience bonus (as expected). Send the unit into combat, the unit doesn't receive experience, but loses units. Retrain the same unit in that Casse city, and it will receive another experience chevron after training. The building should only ensure that units have a minimum of one experience chevron.

EDIT: Forgot to mention, playing EB 81a in BI with Hull's CTD fix.
Chevrons increases (and decreases) can happen randomly during unit retraining. If you have a sample size of one, that doesn't prove anything. However if you run five or ten straight units through that field of games and EVERY ONE of them gets the increase, then it's bug. Please test that out and tell us how it went.