Just showed my Standard Multi (Liège-Visé) and regular ticket (Visé-Maastricht) to SNCB train manager. All fine.

Doing that - two tickets for different parts of a trip on one train - is not allowed in France. Although I just got a ticking off when I have done it in France, not a fine…

@jon There used to be a UK rule that it was OK if the train stopped at the station where they changed over (because you could theoretically get out and in again). I can't remember if that still applies.
@po8crg Sure. That’s what I was doing. Train was Lyon - Nuits-sous-Ravières. Train stops in Tournus. My tickets were Lyon-Tournus and Tournus-Nuits.