Here's additional info:
* I have an HP TC1100.
* It's not just words that disappear. If I make simple strokes, they
disappear too. If I write in an asian language, the strokes of the
characters disappear in the order that I wrote them as if they're being
parsed for recognition while the "ink" is drying.
* When this happens I don't see the shaded "show ink groups" area, even
though I have that feature turned on.
* The last time I had the problem, I had opened and closed several programs
open, including Outlook, Thunderbird, Gobinder, Media Player, Adobe Reader,
and few IE windows. Closing all other applications didn't solve the problem.
* The problem goes away after I reboot. (When things go well, I use standby
and reboot roughly once a week.)