DWU2 Loc: Phoenix Arizona area

I spent some time today combing through my Lightroom keywords. I deleted some unused ones, and moved some into a hierarchy by dragging and dropping them. All went well until I was about halfway done. Then, I could no longer drag and drop. I first tried stopping and restarting LR, then tried cold booting my PC, then I reoptimized my catalog. It's still balking. Any ideas as to what to try next? As far as I can tell, LR is otherwise functioning fine.

Also, maybe a related problem - even with many keywords moved into hierarchies, I can't scroll down far enough to see the keywords in the last few letters of the alphabet - in the keyword list, I can only see partway through the "T's". Does anyone have a fix for this?