I've noticed this since the update that gave Death Dog the siege passive. Both the blue Angel and the Death Dog now remove all effects, regardless of time left.
My understanding is that each turn, the ability should cut one turn from the duration of positive effects, I.e. one turn effects disappear but two turn effects stay on for another turn. If multiple Siege casters present, then two turns get cut etc. This is how it used to work before and it was fair. Now the ability is overpowered (IMHO) and in any case it doesn't match its description. Death Dog and blue Angel are very common in later stages, so this is impactful.
Also, the ability should go away once I kill the caster, and right now it stays on for the entire battle. All passives go away after death and this one used to go away too. This is another bug, I think.