I've got a classic trim '07 Octavia, so there's no central fuel flap locking - you push the flap to pop it out and then push to get it to lay flat.

Its fine generally but when I took it to a car wash the brushes managed to lift the flap away from the body and thrash it around. Having recovered from the shock I took a look and there doesn't seem to be any spring or other mechanism to hold the flap down flat against the body - it just rests against the black "button" that pops in and out when you push it. Is this normal, or is something broken?

Mine clicks shut when you press it in. A second press opens it again - a sort of toggle . If its not staying shut then something is stuck or broken.