A couple more bits of data...
I think these UI lockups happen more frequently than people realize, since they are "self-repairing". I made a five hour road trip yesterday, and there were four UI lockups that I noticed and no idea how many others went un-noticed.
Interestingly enough, my last lockup was in progress when I reached my destination, and that was when I got a repeat of a puzzling problem I had experienced before: when I turned off the ignition, the player stayed on, but I think the amplifiers were off because instead of music all I got was a quiet low-pitched buzzing sound. Pulling the player from the sled to force a re-boot fixed it.
tanstaafl.
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"There Ain't No Such Thing As A Free Lunch"