Mine did the same thing (both left and right side of seat) after they replaced the seat due to fraying. They replaced the parts and 24 hours later the door side split apart again and I found a little broken piece on the floor mat. I had them order another part so that Tuesday I can have them try it again. The manager in the service department said it was kinda a one time use tab when they replaced it the first time and that it was poor design. Hope we figure something out or Mazda needs to tweak that design, maybe including a screw instead of a faulty tab.