Weird KPW blank home page problem

[Stingo]

I have my KPW pretty loaded up with books. I had it in airplane mode (forgot to turn it on from a flight this week). I also have the font "hack".

This morning I went to the home page from a book that I was reading and, apart from the menu icons at the top, the page was empty. I clicked the menu and the menu scrolled down but the typical line around the menu was missing. I rebooted and the problem was still there. I changed the view to cover view and blank boxes appeared with no text. I clicked one and that took me into a collection. Within the collection I was able to see files in list mode but once back out in the home area the screen was black.

After a hard reset that wiped out my content and reinstalling of books everything was fine.

Any idea what happened? Don't want to go through the headache of reinstalling everything again.