I think I may have solved it?
Applied the following, apparently ancient advice of Robert's - - no idea what or why it worked:
"Properties ==> Program tab. Make sure the box at the bottom that says "Close on exit" is **checked**. Cmd line should say C:\XY4\EDITOR.EXE /e4000. Working should say C:\XY4. Batch file should be empty. Shortcut key None. Run Normal window. Memory tab: Conventional mem Auto, Auto; Expanded 5120; Extended None; DPMI Auto. Screen tab: Pick your preferred Usage, check everything else. Misc tab: UNcheck Background Always suspend and Mouse Exclusive mode. Idle sensitivity slider in the middle. Leave everything else as-is. Pick a font you like. Apply everything, OK to close the Properties window."