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?
GarageBand for iOS 2.0: Restoring purchased instruments and sounds
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.
GarageBand for iOS 2.0: Restoring purchased instruments and sounds
Installed garageband with ALL instruments for FREE on iPad Air but..
if you are sure, there is no problem with the AppleID, contact Apple Support:
How to report an issue with your iTunes Store, App Store, Mac App Store, or iBookstore purchase