The APC spawns a NEW unit which is the heavy infantry, not the current infantry which are the regular footsoldiers. I would assume the heavy infantry will be locked to the APC similar to the paratroopers being locked to the transport plane.
It's you guys who don't want to face reality. Game development takes time. You can't simply yell "fix this nexon/BHG" and then expect a patch in a week that fixes it. Nb4 has already explained why the fix takes a while, be happy that they are at least fixing it.