As far as I know it is not possible to detect this (until update 1.7).
Maybe now, with the new weapon skills etc. API someone could:
-build a list of spells which will draw your weapon.
-check if the spell affecting you is in the list
-check if the spell caster is in your group
-> If not stop drawing your weapon
But:
I think it is not possible to stop the weapon drawing by help of addons. Only if you are using the alternative eso client/starter which is able to alter protected functions somehow (correct me if I'm wrong).
And in addition:
You wouldn't draw your weapon then if someone attacks you in PvP, or PvE, if the skill in the list is used
So in total I'd say you must live with it :-(