Even though you can reason why the correct answer is the only one accepted, I agree that these kinds of issues should be dealt with - it's reasonable to presume that the picture above is a valid solution. There shouldn't be solutions like this (and the one in the sound wave puzzle) that seem like they're ok but aren't, because the game interprets the rules differently than a player might.
Hot hawks had another similar issue. Also in the chair puzzle you were able to assemble the picture upside down, which wasn't a valid answer. The puzzles should be designed so that you don't have answers that might reasonably be mistaken for the correct one.