The disc brakes in the Mazda Protegé5 are single-piston floating-caliper design. That means that there's only one piston and it's operating on the inner pad. The reaction slides the floating portion of the caliper the other direction, and it's this motion that applies force to the outer pad.

The floating calipers slide on two pins. The lower pin is removable (10mm socket on the rears, 8mm Allen wrench on the fronts) allowing you to swing the caliper around the upper pin and out of the way in order to replace the pads. The upper pin is a fixed pin inserted into a hole in the caliper and sealed with a bellows-shaped rubber boot.

On three different occasions over the years, I have now found three of my four brakes with seized sliders. Obviously, I should check the fourth! It's always the fixed upper pin; the inside of the hole of the caliper that it slides into, rather than being properly greased, is full of rust. One might conclude that the boots are bad, but all seem to be in good condition. Either water is getting past those boots, or these things were lubricated with water from the factory.

Seized calipers aren't necessarily noticeable. They can cause the brakes to bind a bit, getting hot, prematurely wearing out your pads and reducing your fuel economy. In one case on mine, they caused a noticeable scraping sound. But otherwise you might have binding calipers and not know it.

Anyone replacing pads should notice the problem, because the caliper is much more difficult to swing out of the way than it should be. But will the shop doing the service notice and address the problem? I dunno about you, but I don't trust shops that far. If they can move it at all, even with massive force, they might just put it back together and fuggetaboutit.

Seized calipers are really easy to fix yourself, though. Once the caliper is swung up, you can slide it in the inboard direction and completely off the upper pin (presuming you can move it at all, which one way or another you're gonna have to. Use force as necessary.) Remove the boot (once off the pin, the boot comes right off), then clean off the outside of the pin and the inside of the hole until both are smooooooth. A rifle cleaning kit is helpful cleaning out the hole. Apply brake caliper grease to both, but don't leave too much in the hole because it'll act as a piston and restrict movement. Apply a bit of grease around the ID of the boot, too. Reassemble, making sure not to damage the boot sliding it back onto the pin. When done, the caliper should freely slide on that pin.