The bug

Blocked shulker boxes can be opened in Spectator mode, but blocked chests cannot. Regardless if the intended behavior is that blocked chests can or can't be opened in spectator mode, one of these blocks is not working as intended.
(Although personally I would really favor blocked chests and shulkers being able to be opened in spectator mode rather than not because not only would this be really useful for making redstone/hopper contraptions but also it makes sense as when you open a chest in spectator it's more like a 'peek inside' rather than opening the lid which is the part of the chest that is supposed to be blocked anyway)

How to reproduce

Place a block on top of a chest / shulker box, go into Spectator mode, and attempt to open the container. Currently, the shulker box can open but the chest won't, which is quite inconsistent.