Bosses cannot be frozen during attack animation

The fact that bosses cannot be frozen during attack animation is quite frustrating. For example, I play a Cold Snap build with Cold Bomb, Ice Nova and Freezing Mark. During Tor Gul, I had the boss at 99% freeze buildup for TWO MINUTES but since he *never* stopped doing attack animation I was unable to freeze and therefore, unable to use my Cold Snap, which is supposed to be my big dps since it's a "payoff" skill.

This makes it quite annoying when your build just stops working altogether.