Just a hint: Its not a bug or fraud but a feature.
Buying nothing with nothing sounds like a fair deal. Paying the arbitration fee is payment for a service, not for the exchange, so that’s separate. Looks like a feature to me, though I won’t use it much.
To see what it does would require probably to paste the transactions as well…
But what is a feature which would be very useful for Bisq and privacy?
Were both bisq wallets funded by the same wallet? (Well done I’m really confused) 
Haha sorry, was not intention, but at least i sparked some interest 
Here is the solution: