I did a few Trials earlier with a Biting Wind kinetic bow and a Seven Seraph shotgun as energy weapon.
I was starting with the usual 2 rounds on the shotgun, keeping them for close range fights. Using my kinetic bow at first, when I was switching to my energy weapon shotgun to finish an opponent it was out of ammo. Dead in no time, next round start, have my usual 2 rounds in the shotgun, start a fight with the bow, switch to the shotgun... again, out of ammo.
It looks like a bug, unless there is a skill that remove or steal ammo that I'm not aware of?
(And as a side note, I'm still amazed to not find a search box on these forums, like one you find on all the billions other forums on the web..! Unless there is one that I'm not aware of?)