Didn’t get any answer still, but in the meantime I build a simple work around. maybe if anyone got stack like me it could help:
instead of using the Collapse Transformation feature I added the bkg as a 2D layer. (not pressing the 3D enable button), and just linked the Camera Position and Point of Interest of the camera to the camera in the General comp. that way at least I need to worry about one camera while the other will automatically be updated in the pre comp as well.
hopefully this is a temporal solution.
have a good one in the meantime.
Ido.