I might be wrong, but probably your control scheme (which makes the player "look at" the mouse) is not compatible with "rotating the camera to where the player is looking at". This is because BlackBulletIV's code does not take into account the camera's rotation when returning the mouse coordinates.
gamera does take this into account, so it might help you with that (hump's camera also does it). However your control scheme will still not be compatible with it - you will need to "gradually adjust the roation of the camera so that it matches the player angle", not "set it to the player angle". Otherwise it will be too abrupt.