invite a friend to this app

issues with FB Friend and FB Rules...

i have setup a rule to fire when: "UserA accepted UserB Facebook invitation"

but it does not run....

user-A invites user-B to install this app

user-B logs into facebook and clicks 'accept' on the invite

user-B gets taken to this url:
fb_friend/accept/module/fb_friend_invite_app/delta/fb_friend_invite_app/next/page&h=oAAHSHbCU

then user-B is redirected to homepage

but no rule is run?... and user-B is not logged in to the site.