I've seen that page-frozen-with-dictionary-underline bug occasionally too, but thankfully it's pretty rare. Probably a glitch with the touch screen as PeterT says. Powering off is the only way I know to fix it.
I've decided that my pet peeve with the KT is the inability to go to a specific page number in the book. The slider is much too insensitive - it can barely position to within 20 pages with the most careful manipulation, and then it can take up 60 page turns to get to the right page (at 3 KT pages per book page for some books). Have I missed some obscure means to do this added in some firmware update?