Cloning two single chests from source creates double chest at destination

The bug

When using /clone to copy chests, they will merge if possible, disrupting the arrangement of the original set of chests.

How to reproduce

1. Facing west, place two chests to form a double chest
2. Place another chest to the left of it
3. Break the right half of the double chest, leaving you with two adjacent single chests
4. Stand on top of the left chest
5. Run this command:

/clone ~ ~ ~ ~ ~ ~1 ~ ~1 ~ 

→  The cloned chests one block above have merged instead of remaining separate