I'm curious about this, with apologies. The GLA-MCO booking is cross alliance (Star Alliance connecting to One World) which, while certainly not unheard of, is different and will involve a terminal change at LHR.
All the flights may be on the same itinerary (i.e. piece of paper produced by an agent) but it may be worth checking that the fare is actually a GLA-MCO fare, and not several component pieces bolted together to appear to be one?