Cosmic Creeps emulation glitch?

[Chris++]

Cosmic Creeps doesn't seem to emulate properly in Stella. There's always the chance that I'm missing something about the game-play, however.

 

According to the manual, the level is supposed to advance (signified by a newly full planet at the bottom) when the player reaches 5,000 points. This doesn't happen, however. It's the strangest discrepancy I've ever noticed, as there's no problem with colors, collision detection, speed, etc.