Flag dont collide with the head?

Hello
I have problem with the colliding. My flag dont collide and slide down on the head. Why

Can you give me some advice.
Thanks
Karl

http://www.pasteall.org/blend/9199

try with weight paint.

If you look at my blendfile you see I try use weight paint.
I have made plenty of colliding objects without any problem before. http://vimeo.com/27329859 Maybe the problem this time is the eyebones or shape keys
Thanks
Karl