kubi reports that if an asteroid group has the spawnMax field, it limits the total number of asteroids that will appear per scene change, even if they are allowed to go untracked and disappear. The limit should apply to the total number of tracked and untracked asteroids that exist at a given moment.

I suspect this is actually a side effect of #44: because all the code assumes that spawn rates do not change with time, once the total spawn rate ever goes to zero, FixedRateSpawner will no longer try to spawn asteroids.