Recently the "bug" described in https://bugs.mojang.com/browse/MC-5951 was "fixed". Actually this was a feature request and not a bug - and a one that doesn't make much sense and breaks existing contraptions. This should be reverted and set to invalid.

As you can see in the screenshot the comparator does not respect any other input than a trail of redstone dust. Any torches/levers/pressure plates or anything else do not register at the negative input. Previously this was also the case for redstone blocks.

Some existing redstone contraptions rely on this behavior, so those get broken by this change. Comparators were never intended to work this way, so please revert!