This is not a bug, I think it works as intended. However:

I think that the animation of the cracking double chest is not consistent with the animation of the cracking door.

When I mine the door I see the cracking animation on half door, then I get "all" the door "from two blocks".

When I mine the double chest I see the crack animation on all the double chest (2 blocks), but then I get only one chest.

I think there at least these options:
1) apply the cracking animation on all the door
2) apply the cracking animation only on half of the double chest
3) get 2 chests when breaking the double chest.

Personally I would prefer both the options 1 and 2