I have several simple "Overflow Proof Sorters" in various places around a world. The ones that have redstone going across a chunk border do not behave consistently, but it appears the ones all within one chunk behave normally.
Edit: Much easier steps to reproduce. On my device this seems to cause the bug about 1/3 of the time. Steps two and three are not required, but seemed to make the bug happen more frequently.
1. Create a door (1174, 5, 15) and a button (1175, 6, 16) and a pressure plate (1173, 5, 15). See doorandbutton.jpg
2. Delete and replace the pressure plate.
3. Step on the pressure plate and walk through the door.
4. Travel to 1174, 5, 71.
5. Save and exit.
6. Try the button and it will be likely to not work. You may have to repeat these steps several times.
Old and less clear Steps to reproduce:
1. Create an "Overflow Proof Sorter" (see attachment "overflowsorter.jpg" or similar design on https://minecraft.gamepedia.com/Tutorials/Hopper) that has redstone crossing a chunk border. It is probable that many other devices show the same behavior.
2. Do things Unfortunately I have been unable to reproduce the behavior with simple tests such as unloading and loading half the machine. It seems that if you play and dump items into the machine above for a few hours it will break pretty consistently, but the exact details of how it breaks remain elusive.
3. Come back to find a powered repeater powering a block with a torch on the other side that is also powered (see attachment "oops.jpg"). This is bad and breaks things; everyone is sad.
4. If you break any of the redstone dust on top and simply replace it the device will start working again.