Alright when barbarians are fortified in an encampment every other turn the barbarians will switch between 50% fortification bonus and 25% fortification bonus, then back to 50% and then 25% and so on. When you end a round the barbarian units go through an animation that looks a lot like they are fortifying, which I believe when they do this t the end of every turn they loose the fortification bonus because the code counts it as an action.

Also barbarians do not heal, I am not sure if that was intended or if that is a direct side result of the above where the code counts the barbarians as taking an action when they fortify themselves every turn and thus do not heal.

Hmm, the not healing is intentional by the devs to keep the barbarians weak.

I have noticed the fortification bonus changing... my best guess is that it's caused by the way they're making the barbarians not heal.

Another nice catch!

Load save.
Look at barb fortification bonus (25%)
Space bar warrior. End turn.
Look at barb fortification bonus (50%)
Space bar warrior. End turn.
Look at barb fortification bonus (25%)

Rinse & repeat....