Latest steam version , new game , normal play , 4 ufo down , researched laser , build 1 laser , assigned to soldier , not getting auto loaded , only 1 ammo , got loaded in ufo recovery
build second laser , had no ammo so didn't use it or tried to unassign the first laser and ammo , did read post above so did this try :
started a new game ,no fighting , researched laser , build 3 lasers ,assigned laser got auto loaded and ammo got unlimited sign as long as i didn't move the ammo itself from the belt menu in a soldier his belt .
work around , unload ammo from laser when assigned to soldier and drag it into belt , unassign laser and assign laser again , still got autoloaded and unlimited sign still there and the one in belt also , repeat same procedure for 3 soldiers , al had now loaded laser and 2 ammo in belt , belt menu still has unlimited as long as i don't move the ammo from belt menu ;-)
game time ended couldn't test more