Ok, there has been a discussion about this over on g6performance.com.
Here is a copy of the service bulletin one of the guys there dug up:
#PIC4509A: Radio Displays Changer Parked Message - keywords battery CD display int intermittent intermittently no owners park radio - (Dec 27, 2007)
Subject: Radio Displays "Changer Parked" Message
Models: 2004-2007 Chevrolet Malibu
2008 Chevrolet Malibu Classic
2005-2008 Pontiac G6
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This PI was superseded to update models and model years. Please discard PIC4509.
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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
A customer may comment that the radio will display a "Changer Parked" message intermittently at times, and there is NO explanation in the owner's manual for this message.
Recommendation/Instructions:
This message will display after the CD mechanism has initialized or when you manually park the CD mechanism. Initialization occurs normally upon a battery reconnect. The mechanism will unpark itself once you press the CD load button.
Note: After pressing the CD load button, you will NOT get a message that's it's unparked.
