Well, I really appreciate the help, but I've tried everything I can think of now. There's nothing unusual going on with my screen or computer except that I'm using Spaces -- but I had this problem before I started using those, too. I downloaded the latest version of LibreOffice; I changed every setting I could find (but couldn't really find anything relevant); I tried creating a new file instead of working on one that was converted from Word... all for nothing. So I have tried Google Docs and decided to use Docs for these files that need heavy editing and conversion to and from Word.
I'll lose a couple of helpful features from LibreOffice like the Find bar, but the Find bar wouldn't tell me how many instances were found or replaced in any case. The Alfred shortcuts will save me a ton of time and typing when working properly. Docs doesn't require me to save in a special format while working and export when done, and I had trouble recently with a particular file that showed overlapping letters in LibreOffice until the sender removed the tables. Docs opened it without a problem. I can still use LibreOffice for spreadsheets that I'd rather keep on my computer than in the cloud...
Thanks again!