This man speaks the truth, the shadows do indeed give it away, the diagonal connecting rod has been cut in such a way that at that angle it lines up perfectly with the edge of the other upright. Seen enough of these to know what to look for, it's only a matter of time before you find out why they can't work.
both of you are kind of right but it isnt the shadows... i didnt know but my dad did after 30 secs of looking at it he is an antique dealer and does restoration. basically if you look at the middle piece of wood you will notice that the right end bit is out of poportion to the middle sector. there are 2 pieces of wood! i used a bit of ms paint to explain