...Meanwhile the ExpertFlyer help desk has shown me that if I search on LA specifically, rather than OneWorld, I get accurate results. This is a tip for others too (although it looks like a bug to me)...
It looks like a bug to many but EF isn't inclined to look at things that way. This issue of EF reports giving one set of information when searching on airline X and another when searching on a wider filter (that includes the same airline) has been present on EF for as long as I can remember.