grin Dogscoff. I don't know for sure it would break SE4, but don't count on it running through on PBW.
Someone once posted a screenshot of a combat where there were more ships then squares on the combat grid. What happened was the game placed ships on-top of each other. You couldn't move a ship on top of another, but the game will place them there if it rounds out of room setting up the combat turn. I assume it would do the same thing in the case of planets.