I built a spaceplane in the SPH that looked like it should fly. Put 'Thud' type engines on it so I could maneuver in space. With all fuel removed from the rocket engines, the COM and COL looked good for atmospheric flight. Plan was to use rocket boosters to get to space, the thuds to help line me up on my trajectory, and then a long glide path back down to my destination.
However, once in the VAB, my COL shifted to a point near the Thud rockets - well behind and above my COL (were I in level flight). You can imagine my flight char... okay, there were no flight characteristics - the plane didn't fly. I got it into space, and only killed a few fish when I crashed into the ocean.
Is there a rational reason behind this - or is this a quirk of the game? I figured that once the Thuds were out of fuel, and the plane back in the atmosphere - I figured the COL would shift to where it showed me it was in the SPH with all fuel empty from the rockets...