From the information I found on a Interlude database this is what the skill is meant to do;
Magical Mirror Lv.1
A shield power that has a chance to reflect de-buffs from magic skills back to the attacker. An equipped shield is required to use this skill.
In reality it reflects both buffs and debuffs which makes it somewhat useless unless you're on selfbuffs only (Only in olympiad). Is there a way to make it only reflect debuffs or is this the way it's meant to be? I can't really remember how it used to work in Interlude.
it reflects buff aswell.this is the code
cal_mirror1] skill_id=351 level=1 operate_type=A2 magic_level=78 effect={{p_reflect_skill;0;10};{p_reflect_skill;1;30}} operate_cond={{equip_shield}} is_magic=0 mp_consume2=36 cast_range=-1 effective_range=-1 skill_hit_time=2 skill_cool_time=0 skill_hit