Nook Simple Touch Hung on Update

Found my Nook Simple Touch hung this morning in an update. Unclear when this started, some time over night. The Nook was plugged into the charger all the time.

After about 10 minutes I decided that the "Please don't turn off your NOOK!" is nonsense, because nothing was happening. Note that the progress bar at the bottom was not animated and appeared somewhat mispainted.

After holding the power button at the back of the device pressed for at least 20 seconds, the device power cycled and went through a bootup cycle which almost immadiately entered the "Installing..." display again. But this time, the progress bar at the bottom was animated, slowly filling from the left. Then it switched to another startup screen, the progress too about 2 minutes.

Finally the usual screen saver appeared. I could unlock the device, and the main screen displayed a notification icon regarding a software update. The time of the update is the time of the power cycle.