baselb - so you've had an encounter with the rottweilers who guard the realm of BMI check-in desks.
I've encountered them myself, particularly at Manchester, where they don't have a segregated business/silver/gold check-in area. So when I'm asked in a sometimes supercilious tone 'are you flying business class?', I politely respond with a 'I have a gold card' as I continue to the desk without breaking my stride.
Although it seems a little gauling at times, I suppose its just a case of protecting the value of their commodity (in the same way that they wouldn't let you sit in a business seat just because it wasn't going to be occupied).