Speed reload is a new feature.
To perform a "classic" reload, tap "X" (on Xbox) or "Square" (on PS) once. This will reload your gun while keeping your ammo.
To perform a "quick" reload, tap the same button twice quickly. Your character will throw out the current mag, so you will lose the ammo that was remaining in it.
It's in fact very simple to test. Go into a private match, look at your total number of ammo (in mag and in reserve). Shoot 1 bullet, perform a quick reload, and look again at the total number of ammo. Do the same with a classic reload, and you'll see the number is not the same.
Edit:
As said by @Chantola, this might be broken at the time, and you should expect a fix in the next update.