Comment 1 for bug 377994

Doing more research, evidently this was a "feature" in prior versions that wasn't at least in some cases actually working - might be why I never saw the behavior before. It can be disabled in the pertinent rc file (e.g. /etc/joe/jstarrc) by entering under "Default local options"

-french

over at the left margin. Somehow single spacing between sentences is considered to be "French." I've tested and this does make the "feature" go away. I'd suggest this be added to the defaults in the various rc files in the package.