One more interesting fact about the brightness bug, perhaps: I'm running iOS 5.1.1 on both iPad 3 and iPad 1, but the brightness bug behaves differently in Marvin on each of them. This is true both when the iPad's auto-brightness mode is activated and deactivated.
On iPad 3, putting the iPad to sleep resets the brightness in Marvin to around 68% every time. But on iPad 1, the reset value is around 80%.
If brightness is set to 0% on iPad 1, it resets to around 40%, whereas it resets from 0% to the usual 68% on iPad 3.