Please find a link (via Dropbox) to a world where, with the latest beta (as of this writing), there is a pair of small chests. Lift the right chest (it has less stuff in it), put it back down to merge into a double chest (and replace its contents), and then exit the world.

Re-enter, and it will be a pair of single chests again.

https://www.dropbox.com/s/81xmvui5j4pw0jt/Patience.mcworld?dl=0