(From a discussion on the French name "Jean-Loup" / "Jeanloup" and whether it might be a variant of "Jean-Louis" rather than related to St. Loup)
Perhaps some smart cookie in the 30's or 20's wanted to name his newborn brat "Jean Lou" but, not allowed to do so given the stringent laws then in effect, called Saint Loup with a p to the rescue. There are stories of boys being named "Maure-Pie-Yon" ("morpion" = crab louse), "Désiré-Jean-Doute" (wanted? I doubt it), and girls "Belle-de-Nuit" (using the Republican Calendar), all legal names, since there is a Saint Maure, a Saint Pie, a Saint Yon, and a Saint Doute, and technically the "saints" of the Republican Calendar were rumoured to be acceptable.
I especially like "Désiré-Jean-Doute" :D