Don't worry, clearly bungie is going to make Ice Breaker lose all ammo when you switch to a different special weapon. Mark my words, it's obviously going to happen. And it should! Ice Breaker is my favorite PvP gun and people are abusing it to get ammo for their Easy mode sniper. Here's how you're supposed to use ice breaker: https://youtu.be/cdKOTKN84_U