There's no gap, it's just the single corner the puzzles share is the size of the piece that should belong to the black puzzle, which is smaller than the piece that should belong in the white puzzle. Therefore it looks like the white puzzle is missing a corner, when really that corner is just really small, smaller than expected anyway.
But clauswe, I would argue with your fully functional claim.
Each puzzle is fully functional, PROVIDED the other puzzle is not in the way. But now is that REALLY fully functional?
Your call I guess
The puzzle actually does look very nice in two colors of plastic. Well done!