I thought he was aware of his magic being in effect?

He must be too caught up in the moment. He can notice a de-spell, but it's as if the spell didn't work in the first place.

I hope it leads to something interesting x3

I brought it up since Seglagg knows if his magic activates or not lol

It kind of is a plothole though, now that you bring it up. He usually knows it's been despelled because someone is like "hey, who is that?" Or he purposely gets someone's attention. It's kind of like if you're invisible, you won't know if you are or not unless you can see yourself or something.

i think it goes back to how the magic opperates for each caster that medrash needs permission to affect others and seglagg doesn't. Seglagg's is more infectious like that and he needs to sing or play music to use his, so he is consciously aware of it too. medrash's is more passive and friendly that he needs permission and therefore he relies on others to get confirmation that his magic is active. You could also equate it to spell caster level as seglagg has been doing magic for probably much longer than medrash has.