I seem to have found a limit in the number of sun I can collect in Plants versus Zombies. Clicking on suns does not increase the count, but healing walnuts decreases the count.
Once I replaced the walnuts and sunflowers with frozen watermelons, the game turned into a near perpetual motion machine -- killing zombies as fast as the game added them. I let it run for about an hour. ;)
Is there a problem here? Probably not. Anyone playing this Seeing Stars game to win would have added the last star long ago; but as a tester, I wanted to see what would happen. ;)