Frost Shield counting down during pause

The frost shield duration still counts down during a pause (merc, menu, and passives screen). It lingers at 0 seconds for what I assume is it's expected life time, but the frost shield HP bar does not move when taking damage and I am not sure if it is functioning correctly.

EDIT: It also doesn't seem like frost shield works at all verses Mercenaries, even with duration left or stuck at 0.