I'm not sure if this is the sort of thing you're looking for - a single track main line and a loop? I'm not so familiar with the WHL so this could be what's happening there too?
On the Highland Main Line for example, at Dunkeld northbound trains run 'right hand' but only in the circumstances of there being no crossing southbound traffic. If there is a cross then the northbound train is placed in the Platform 2 loop, and the southbound runs through or stops on the main line left hand. Platform 1 runs both ways, but the loop only northbound.
If you only ever used or passed through the station on non crossing northbound trains you'd be given the impression of RH running.
I believe most, if not all, passing loops on the Highland Main Line are in fact bi-directional so that trains not required to stop do not need to slow to negotiate the crossovers, but can run through either at or close to line speed. This is why the morning down sleeper, at Kincraig and Tomatin, appears to enter the loop wrong-line- allowing southbound traffic to pass seemingly wrong-line without needing to slow.
When making a station stop, unless crossing another train, trains always seem to use the track nearest the station building or main station entrance for the convenience of passengers- saving passengers the need to cross a narrow footbridge. This is certainly the case at Dunkeld, Kingussie and Carrbridge.