It's possibly just that the system doesn't know how to handle it when an aircraft doesn't have CE from the get-go, and it's just used to holding the first 3 rows for potential CE sales until t-72? I know most CityFlyer flights will usually have a CE cabin (GLA-BHD is one of the few that they don't sell the cabin in), so it's possibly just that. More a curiosity for me than anything else, but certainly likely to be the case that the system gets confused and given that BA likely won't be operating these shorter ET-only flights for more than a few more months, not worth expending time and effort to resolve. This flight currently appears almost empty, so I'd even wondered if it might have been to trim the aircraft, but the back rows weren't blocked, so kind of knocked that on it's head.