I think that's a bug with flaps when they get damaged while extended. No ill effects if you leave them in the position they got damaged in but raise or lower them and you get what you experienced.
The missing flap is still present and locked in the position it got damaged, just can't be seen.
Not certain, but I think this applies to all planes, not just the D11.
At least that's my interpretation of it, I could be wrong.