ok ive experimented with the settings and have found this happens when i let it sleep while using ibooks.
I use my ipad ot read alot at night before bed and then just leave it to turn of with the auto lock.
was wondering if there may be a bug with the ibook app for the ipad that cause the screen to dim prior to sleeping, then brighten without interation, then dim and then sleep.
It happens in that order. dim bright dim sleep
but when i leave the ibook app and leave it on the normal home screen, the ipad dims then sleeps normaly.