Ground Combat Problem (Bug?)

I am having a problem from time to time where my invasion troops seem to be placed outside the map for ground combat. At the end of each turn the ground combat screen for that planet comes up and the enemy troops just mill about randomly until the timer runs out. I can't see my troops anywhere on the map. After combat I look at the planet and can see that they are listed there as occupying troops but I can't do anything with them. I can reload them onto my ship, and since they are on the planet's surface I can just simply slag the planet and move on. I have tried making 2nd drops and the additional troops also get placed off the map and the cycle just repeats itself until I get tired of it and start a new game. Has anyone found a way to clear this endless process?