Steps to reproduce:

1) Put down a container (a barrel for example). Put 3 diamond swords in it.

2) Stand on the container and run this command:

execute if items block ~ ~-1 ~ container.* minecraft:diamond_sword[minecraft:count={max:1}]

Result: The command succeeds with "Test passed, count: 3"

Expected Result: The command should fail. The amount of diamond swords in the container is more than 1.

This seems to be happening with unstackable items. Stackable item checks work fine.