Originally Posted by
flyingbee
IIRC, the extra oxygen mask is a 4th mask for a group of 3 seats (ET or domestic config) but on BA not all rows have the 4th mask. But in CE where only 2 of the 3 seats are sold there shouldn't be a problem because all groups of seats should have a 3rd mask that could be used by the infant due to the convertible seating that will allow 3 people to sit.
However, the seat selection tool might not realise this!
That's exactly it. On the ABC side most short haul aircrafts have the extra mask on odd numbered rows, and for DEF on evens. So am surprised you cannot reserve 2DF. Different configuration on this exBMI aircraft obviously.
As
flyingbee mentioned, the seat selection tools does not realise you are in CW, and in my experience a phone call won't help.