Canon 28-105 creeps. help!!!

israel, sorry for poor english
canon EF 28-105 3.5-4.5 II usm bought new, 2 months ago in tokyo for full (good) price.
set at ef 28, while pointed down, it creeps toward ef 60. PLEASE HELP ME IF YOU KNOW !!!
1. is that normal in this kind of lens?
2. bad lack. i have got a lens made on monday.
3. i will better do by stop shooting for two months and send the lens to CANON to deal with it

Lots of modern lenses do this. I don't know for sure that you should expect it with this particular lens, but I would not be surprised.

John