In addition, combining two chests with a piston or breaking a double chest with a piston where one of the chests is receiving items from a hopper creates “ghost items” where the hopper is placing items into the chest, but visually they disappear if you close and open the chest again. Comparators stop interacting with the double chest as well.
I can reproduce this by creating a 3x3 “piston feed tape” of chests. Where 1/4 pistons is controlled by a comparator.
I recorded a video of what I encountered with the double chests visually glitching after being pushed by pistons. I think the intended behavior is for them to separate into single chests if they get pushed.
[media]