At GVA if you're accessing FT on the basis of status and not on the basis of class of travel (on BA), the FT gates won't let you through when using the BA app. You need to get a paper BP. I suspect some of the agents (who are now outsourced) aren't entirely aware of this and don't code the paper BPs correctly either. Of course you only discover this once you've gone up one floor and made your way to security. More often than not, it probably isn't worth going back down to get it coded properly, unless you're travelling on a Saturday in the ski season.