i've been noticing this too, but i'm not sure if it happened every time for me.
 it's a bit scary since you're not getting any feedback about whether it's
trying to copy something or whatever.

I'm almost certain its not been every time, but certainly I've only seen it
follow through maybe once or twice.  There are some disconcerting flickers,
obviously not always preventable when resetting cpu's, but they are worrying
when nothing happens after that.

in fact, last night it did a proper cycle, coming back to life within 30s after
firmware update completion

Another disconcerting aspect of the firmware update process is the progress bar
not quite getting to the end. Seems like we may want to put in a delay before
rebooting, just to show the complete progress bar.

Fixed in firmware rev 6. 

Of course, people won't see the fix until the next update after updating to rev
6. :-)