The bug
One single redstone dust powered by either type of redstone comparator and pointing any container that reacts to redstone signal (e.g. item hopper) does not properly connect to redstone components including:
output ends of redstone repeaters
output ends of redstone comparators at the same or lower power level
unpowered redstone dust
redstone torches (only when the dust is at 15 power)
flank ends of redstone comparators
the list above may not be complete
the PP updates do properly cover the redstone dust and can be detected by observer
How to reproduce
Create the setup shown in the image below. The chest should contain a single item, and the bottom redstone wire should be placed last.
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Expected behavior
The two pieces of redstone wire should be connected.
Please verify that this occurs without any resource packs enabled (and no mods).