I'm sorry to say I experienced my first lost key-up today, on beta-10 (consumer). I was navigating the playlist menu when I pressed the "up" key. They key-up event was missed which resulted in the unit backing out of all of the menus and powering off.
This is the first lost key event I have had, the buttons do not appear to be physically sticking.
(I'll send this to the bugs email too)
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Unit serial number 47 (was 330 in the queue)...
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Remind me to change my signature to something more interesting someday