Yes. I was signed with my own ID and used my iTunes credits to purchased it.
I meant, when you tried to "Restore the Purchase" on your friend's iPad. Did you remember to sign into the AppStore with your own AppleID after the update?
The problem is, there are many similar complaints here, if you look through this forum. For me, the purchase did not remove the additional content, but others were not so lucky: It may be a bug.
if you are sure, there is no problem with the AppleID, contact Apple Support: