I have a facebook application that is published at facebook platform and i used facebook API to invite friends and i have succeeded in creating invitation form but the problem is that when u invite friend and send invitation and the invitation request sent to the user and the user accept it this friend appears again in the friend list that can be invited again

For example :

i have friend in my friend list named X and when i send invitation to him the invitation is sent and and X accept the invitation and when i try to send invitation again the friend X appears again in the list that i can select from to send invitation this means that may i send an invitation to this user (X) and he is already playing the game i need to know how to fix this problem so friends appear in the friend list (for invitation )only friends that not use the application.

My application at the following link My Game application visit it and see the problem exactly after inviting friends they will appear again is this normal in any game application?

thanks in advance for any reply