When I use the trigger function "Allow Gun 'A' only for vehicles" to attach a gun to a Hound Walker, Mobile r081, or Drone, some of the guns fire once and then do not reload. The affected guns:
Rocket Launcher CS-LitBro
Lite Railgun v01 CS-HShot
Shotgun CS-DAZ
Sniper Rifle CS-YippeeKiYay
Glock (fires its 10 round magazine then does not reload)
M4A1 (fires its 30 round magazine then does not reload)
Star Defender Rocket Launcher
RPG by lostmydollar
The guns reload when attached to a Corvette.
I created a demo level so you can try it yourself: oystercize-reloadingbug
Use Tab to move from vehicle to vehicle.