Originally Posted by
clubeurope
i.e. as it stands there is no scenario in which this itinerary being sold by Lufthansa can be considered legal or "usable" to any passenger
Agreed. Sounds like it is a pretty universal restriction.
So should LH (and other airlines) go and temporarily change the programming of their flight shopping engine to interdict connecting itineraries at SIN? Yes. Will they? No - it's not a priority and they will still say that responsibility lies with the pax.
Out of curiosity: Have you tried other airline websites and OTAs? Do they offer or hide connections through SIN?