From IRC...

<Lotheric> non breaking space U+00A0 gets changed to a regular space U+0020 once saved Is this a bug ?
<Leftmost> I wouldn't be surprised if it's intentional.
<Leftmost> I doubt there are very many U+00A0 which are artist intent.
<Lotheric> in french it is used before a colon
<Lotheric> unlike in english, there's a space before and after a colon in french
<Lotheric> we're weird like that
<Lotheric>
<Lotheric> non breaking space is used to not end up with a title split like this
<Lotheric> Concerto en mi mineur pour 4 violons, cordes et basse continue, op. 3 nᵒ 4, RV 550
<Lotheric> : I. Andante

http://www.btb.termiumplus.gc.ca/redac-chap?lang=fra&lettr=chapsect6&info0=6.13

https://fr.wikipedia.org/wiki/Deux-points