I had coal stored in a trapped chest. It was being pulled out by a hopper. If I went into the trapped chest gui. The coal that was being taken out was not updating. If I closed the trapped chest gui and re-opened it. It would update. But it does not update while you are in the gui.
Place a trapped chest down. Place a hopper underneath it. Does not matter which way it faces. Put any sort of item in the chest. Open the trapped chest gui. It will not update the gui of blocks being taken out.
Duplicate of MC-6939, please use the search function to see if your bug has already been submitted. Currently over 56% of tickets are being closed as duplicate.