Not sure if its intended or not, it just seems weird to me (and I think it shouldn't be like this) that when, say, it's already immortal "for life/ forever", then we try to add something (can't be targeted for 1 turn) which is less than that then we shouldn't be left with the small thing.
It bothered me cuz I played Reflective Shield, Quint and SoW on the enemy Seraph, and when it used its skill then immediately in that turn it also lost the magic damage property.