As native speaker we also use "ik mag jouw oranje rugzak"
In the future you should report things like that (using the Report a Problem button that shows up when your answer is marked).
It sounds the same like in German)
When you say native, do you mean Belgium or Holland? At the very least, that would not be accepted on an official language test in Holland, it could be that some groups use this form informally, but is it not "official" Dutch.
How does 'mag' translate to 'like'?
Is "ik houd van jouw rugzak" possible ?
This was marked correct for me