Nav reboot at startup?

The other night I got into our 2006 and started up the car. I had shut down the car in the Nav map screen a few hours previously. Upon start up, the MFD just showed the Toyota logo as opposed to the "I agree" screen. After a few moments, I pressed the display button and got the message "DVD loading, do not shut off system." Then finally the "I agree screen" came up. After agreeing, I pressed the voice button and got no response. Then I pressed the Dest button and after a delay, I got the Dest screen and was able to enter home as a destination. There was no vocal confirmation (I can't recall if there usually is or not). After I drove off, everything behaved as usual.

My only theory is that the Nav system rebooted for some reason--we never had this happen with our 2005. The one thing I didn't do was try any non-Nav related functions on the MFD, alas.

Anyone have any similar experience? Is this something we should be worried about? The temp wasn't unusual or anything (except that it was unusually warm out for November). The car isn't being driven as much as our 2005 since we moved to DC--only a couple of times a week as opposed to daily.