Steve,
Like Dick I've had the same experience with my 496 if I turn the Garmin off while it's connected to power from the plane. If the unit is out of the plane turn on/off is normal but if connected to plane power it acts just as Dick said. The unit is actually on but in a dim mode. I bring it back just as Dick describes. I'm sure your unit is also in a sleep/dim/charge mode.
al meyer