Nope, hough you ought to play eith limited ammo anyway IMO, it adds to experience if you have to use the archers properly rather than letting them loose their bows at anything htat moves, also the AI gets unlimited if you have it, and he's better at knowing when to fire anyway, you'll get decimated. Units like Naginnata are pretty much useless with unlimited ammo on.

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It's not a bug, it's a feature