I have noticed a few issues with airplane mode lately. First sometimes it just doesn't transition to airplane mode, it says its on or its off but in either state its no reflecting in the signal meter.
Next issue is each night I put the phone in airplane mode and plug it in to charge, during the night I heard several "droid, droid, droid" sounds from the phone then its quiet (wife is getting annoyed) and finally the best part, since the phone is in airplane mode there is NO reason I should have a voicemail waiting for me since there is no cell signal to get a message with. Yet every morning I have a voicemail indicator waiting. I turn off airplane mode and voila, no voicemails at all.
My wife says, leave your droid downstairs, period.