I was looking at the shops in Varrock and when i traded Thessalia (milestone cape shop) i noticed that i could buy the milestone cape  (50) even though my hunter level is 40.
I don't know if this also happens with the other milestone capes.

Picture showing the shop (also shows the id of the milestone cape (50)):
http://imgur.com/sXKutiQ

Picture showing my hunter level:
http://imgur.com/P2C3XwT