I discovered this bug when I was making a spawn for my creative world. I created an old type of world(not infinite or flat). I made a 5x5 box made out of barrier blocks at the very corner of the world. Then I placed command blocks inside to teleport people out of the box. I tried to activate the command blocks with buttons but it did not work. I checked the command and even tried it in chat and it was fine. I quit and re-logged on the world but found the WHOLE BOX WAS INVISIBLE! The signs were still visible but the command blocks, the buttons and the barrier blocks was there but invisible. I held a barrier block in my hand but the barrier blocks placed weren't showing. I kept re-logging back on but the issue is still there. Please fix this annoying bug.