I was asked to approve a payment in the app, but chose to click the reject option. I was then asked for a reason, and I indicated that it was no longer wanted.
At this point I expected the payment to be rejected, but it immediately went through, and the commerce website I was using updated as if the payment was approved.
3DS is purely a liability shift from merchant to issuer.
We can return a fail result and the merchant can still choose to continue to authorization - they just assume fraud liability at that point 
Could there perhaps be something on the screen to inform the user that?
Bit of a long message to fit in
Happens very rarely as well 
Since PSD2 is soon going to make SCA mandatory online, I don’t think this will be a huge problem going forward