Search is nearly useless when it does work. The fact of the matter is that traveler(s) starting AONE's ex-MRU posted that they had been told by BA/MRU that there was no A availability on their intended travel dates even though it was showing on EF. Iirc A space was made available to them on alternate dates, probably after MRU asked London for it.

I never read any rational explanation about why such a situation existed, including a thread I started on the BA forum. My own guess is that BA's availability is posted to the CRS according to an automatic recipe with less human intervention than one might expect, but they have the ability to insert a check-point in the reservation process on a segment basis that defers to the "real" availability, which on that thin route might be pretty meager.

If it mattered to me personally I would simply fax/email the BA travelshop in MRU and ask them if the situation still exists and what a would-be traveler should do in order to effectively plan travel.

As a further non-sequitor, last summer I thought about booking ex-MRU using IBL Travel rather than the Travelshop, and they promptly booked 3 A seats for me on the date I wanted. (The agents at IBL were uninformed and non-responsive, but I bitc.ed and got the attention of the office manager who seemed to know xONEx very well, and quickly quoted the correct price and was ready to ticket. Only real problem, they wanted wire transfer, although the real show stopper for me was the tedious flights CMB-MRU, misconnecting MRU-LHR, misconnecting LHR-LAX on AA, all of which would have wasted 3 days getting home, where CMB-HKG-LAX arrives almost before leaving.