Please do not interpret three posts in relatively rapid succession as nagging or desperation but I seem to be doing something wrong with my thin spaces.
I have used both &# 8239; (without the space) and   at various points in my French sentence. As expected, their effect is identical. However, their effect is also unexpected!
In Sigil the thin spaces appear as a very bold, fat letter I.
In ADE the thin spaces appear as question marks.
What basic, foolish error have I made now?