For a while, when you selected LHR - JFK and 'Economy (lowest)', for some bizarre reason it would show all of the regular ex-LHR flights, and then the LCY-JFK A318 flights. Looked very odd. Now if they had given me them at the same price I would have been interested...
Not tried it again recently to see if it is doing the same thing. Maybe the software thinks it should just be returning the lowest fare code.