Troops vs. Non-populated colonies

[DirectorTsaarx]

I've experienced the same thing; I've also had occasions where I killed off the population of a colony (as preparation for invasion) with neutron bombs (population damage only) and, as soon as the population is zero, I get a "no planet in range" error if I try to drop troops, and then I get a "combat ended" message. I can attack again, and manually drop troops during that second attack, but strategic won't do anything. I have no idea why it happens...