Lighting puzzle?

[Simius]

A colleague mentioned, yesterday, that there is a problem with her two way lighting system. I've tried to work out the puzzle myself by drawing diagram after diagram to illustrate how her circuit is wired up to give such a scenario, but haven't found the answer yet.
The scenario is :-
Two way lighting for landing light. Switch at the foot of the stairs, switch at top. Her husband wants an early night and switches on the landing light at the foot of the stairs and switches it off again when at the top. She goes to join him but the switch at the bottom doesn't turn the light back on. If she goes to the top though, the switch turns the light back on. (I'm not sure if going to the bottom would turn it back off, I can find that out if needed.Thinking about it, I assume it must).
The common must be there, I think, and my natural thought was that it was in the wrong terminal but I just can't get any of my circuits to replicate the scenario. I haven't tried any alterations to the ceiling rose wiring.
This is a real situation BTW but it seems quite common because another lady said that she has the same problem!

 

[dannyboi2003]

The link between switches (either L1 or L2) is not connected, this is usually the cause of the symptoms you describe. If all connections are sound then one of the switches is probably faulty.

 

[Simius]

That works.
I hadn't thought about actually pulling a wire out, which of course would be the most likely scenario!
Still, I now have a dozen diagrams and outcomes of incorrect wiring of a two way system.
Thanks.

 

[daytona]

or the common one end might not be the common the other,as in you might find the yellow in the common on one switch and the same yellow goes into l1 the other

 

[Lectrician]

Getting the common mixed up with either L1 or L2 would lead to this situation - extremely common problem, pardon the pun!