[v1.10]
I have had a similar experience.
I played the level (4), and when I had about 32 asteroids, I decided I wanted it ALL, so I attacked the remaining asteroids all at once. I conquered them all, but received no 'Mission Complete' message. I continued to take my swarm all around the ring of asteroids to see if there was something I missed. Nothing.
One possibility I thought of was that I moved beyond the requirements of a "win" (registering 34 then 36), skipping the "win" scenario entirely.