Okay, I was thinking about FairyTail and Nalu... I don't know if this is a stupid theory or not. When Lucy was being controlled by the fake salamander's, Bora I think, love spell, Natsu came in and the spell stopped working. This didn't happen to anyone else. What if this was because Natsu was Lucy's soul mate, so to speak. So when Lucy saw her 'true love' the spell was broken.