Flynn-Fletcher Probability Ion Theory
Today I present a theory that spawned through a discussion I had with @doublytoxicwaste. It was an interesting discussion, but here's the end result: I realized that Phineas and Ferb's positive ions give Candace the opportunity to have fun with them (which is what the boys want). If she takes the opportunity, their positive ions will override her own negative ions. BUT, Candace usually chooses to try to bust them instead, which lead to her own negative ions taking over. If she chooses this route, the Mysterious Force (aka the probability ions) will take away the invention before Linda can see it.
Think about it. Anytime Candace actually does join Phineas and Ferb in their crazy fun activity, it goes off without a hitch, and Candace often ends up enjoying herself. (i.e. Dude, We're Gettin' the Band Back Together or Summer Belongs to You) But, whenever she doesn't join her brothers, she only ends up miserable after yet another failed busting attempt.
