Originally Posted by
stanman13
I think it is that way from the factory. Look at the relationship between the top of the seat tube and the head tube. In order for that top tube to be straight, it would have to be a sloping top tube, which to me would be more surprising than an intentionally bent one. Also. the joint of the top tube to the seat tube does not appear to be bent, which it would have to be if the top tube were bent by accident.
I think it's a way for the manufacturer to make a smaller frame size (regarding seat height) without having to make a smaller head tube or change the joints in that area. Just shorten the seat tube and bend the top tube down to meet it.
It certainly did cross my mind that if one bent one tube, it could affect the rest of the geometry on the bike; so we do indeed have a mystery. If I may say so, if one is really curious; there are retro-bike forums in the UK where one might be able to ask.