Chest openable in spectator mode

I made a single-biome world in Minecraft, a "End Highlands" biome. I used the seed "pollinating sandboxes" (hashes to 0) and spawned right next to an end city. I entered it and then saw an end ship nearby. I spectated the shulker guarding the elytra after having opened both chests once, to look what's inside. I watched a while. When the shulker suddenly turned around and shortly directly looked at the chest the crosshair in the middle became visible. When the shulker looked at the chest again I quickly right-clicked and the inventory opened, although the chest's contents were locked in their slots.

The recording was made with the Ubuntu-built-in key combination Ctrl+Shift+Alt+R.

I have slightly modified the JVM arguments but only to give MC mor memory. When I installed a new, completely unaltered instance of MC, the behaviour was the same.