I’d like to make a table very similar to this one. (complete gallery is here: http://opalko.smugmug.com/Woodworkin...7627272_k8cbg3 )

Some call it a pub table, some call it a refectory table. There are 2 leaves that are self-storing under the top.

As you can see in the gallery, it’s a pretty nifty design. The size is 3’x3’ with an extra 1’ on each end when the leaves are extended.
The top is what I have a question about. It’s a frame & panel design. The 4 wide pieces are 8” with 1/2” along the long ends going into a dado in the 3 narrow 2 1/2” strips (on the interior) and the 2 short exterior edge pieces:

The interior strips about 1” thick and the wide 8” pieces are 1/2”. So the top is quite lightweight even though it looks heft sitting on the leaves.
My question! All of the interior pieces float – I can actually move them a tiny bit back & forth. So the only thing glued (apparently) is the 2 short edges tenoned into the long edges. What keeps the entire thing from just racking out of square?!
Final (side) question. My take on the design will basically double the length of the top to 6’ (so it will be a 3’ x 6’ top) The leaves will add another 2’ to it to make a 3’ x 8’ table. Do you see any problems with doubling the length to 6’?
Cheers all -