Just a small edit, not all advanced classes have knock backs. At least my Operative doesn't.. I'm fairly sure that assassins, inquisitors, mercenaries, jugs, and snipers all have at least one knock back. I may have missed a class, though. Powertechs? Marauders?
Mercenaries and sorcerers have a knockback, so all classes have a knockback.
Working as intended.
Not sure what all the classes you mention are. Must be another game.