This is not a critical problem but a surprise. If a chest is blocked from opening with a non-transparent block then it does not receive items from/or give items to a hopper. I even tested this with a cat, which sits on top of the chest and also prevents items from entering-from or exiting-to hoppers. I can see that this might even be a feature with pistons, etc., but I discovered it when I was trying to make a compact structure and while I needed the storage that the chest provides, I didn't anticipate a need to open the chest so I blocked it with other parts of the device.
If you wish, go ahead and label this, "Works As Intended." But at least it should be noted in the Wiki.