I don't have my current copy of D1.3 with me, but I agree with you, that no melt-through is permitted. They should go back and reweld the joint so that there isn't any melt-through showing. The welders know this, they had to take a qualification test for this joint. The melt-through is a place for the deck to start ripping when loaded.
Hopefully someone else with a copy of D1.3 handy can verify this, because I'm going from memory and that is dangerous.