corruption of dequeued UITableViewCells after device sleep

My iOS UITableView based app is working fine until the device sleeps. If the device/app sleeps and then is woken, then the app display is initially fine but as soon as a cell is dequeued, for example because of a scroll or otherwise, the new cell returned is not fully initialised, as in initWithStyle:reuseIdentifier: does not appear to have been properly executed. elements added are still their, but they have lost their positions. This is NOT a problem before the device slept.

Am I missing something obvious?