[Phoenix-D]

"Is this a glitch or intentional?"

I think that's intentional. Those weren't troops, those were *militia*. Defenders generated on every colony, based on the colony's population. Normal troops, you kill them and they stay dead. Militia only stays dead as long as some of your troops survive (i.e. stalemate) otherwise it regenerates; I assume that's the militia recruiting more soliders.

Phoenix-D