Bardin’s throwing axes can have the traits Scrounger and Conservative Shooter. Both traits work properly in regards to giving you ammo back, however if you get a headshot or crit while throwing your last axe your ammo bar will show as 0/1 and you will be unable to throw your one remaining axe until you switch to melee and back again.
This bug also affects kruber’s longbow and possibly other weapons as well. “gun” type weapons like the repeater don’t have this issue because if you get ammo back with your last shot the weapon will begin it’s reload cycle automatically.