I am only speculating, but a long time ago as a young electronics hobbyist I was playing with LCDs taken out of calculators and digital watches and very quickly discovered a disturbing fact. That polarization change is achieved by applying a voltage between two transparent electrodes with the liquid crystal between them. BUT - any segment thus activated remained dark for only a split second before it started fading back to transparent, even though the voltage was still applied. I had to reverse the voltage to activate the segment again. Even worse, leaving the voltage with the same polarity applied for a long time could damage the segment permanently. "A long time" meant something like a few seconds. In short, for a proper operation of an LCD, you need to feed the segments voltage with quickly alternating polarity, in the range of at least a few Hz. Dedicated LCD controllers do this. My understanding is that some electrochemical processes start happening in the crystal if you don't.

It is possible that the forced power-off disrupted this alternating current mechanism and left the pixels activated for longer than their healthy dose with the same polarity voltage. By the sound of it, the damage was not permanent but possibly long lasting.