I think this bug is similar to how dispensers, droppers, and pistons BUD, but it also affects other redstone items*. This happens when you redirect a piece of redstone that is on a transparent block such as an upside down half-slab or a block of glowstone. Note that the redstone on the transparent block has to be directly powering the redstone component*, and it also has to be redirected to another piece of redstone this is one block below it. If done successfully, the redstone component* will not change state until you give it a block update.

*such as repeaters, comparators, torches, hoppers, lamps, doors, fence gates, and rails

Steps to Reproduce
1. Place down the desired redstone item*
2. Place down a transparent block (e.g., upside down half-slab or glowstone) next to the redstone component*
3. Place down redstone on top of transparent block
4. Power the redstone
5. Redirect the redstone to another piece of redstone to the side, and one block below it

EDIT: This "bug" seems to be "fixed" in the new Minecraft 1.13 snapshots. Currently in the snapshots, if the redstone is on a transparent block, it will not redirect to another piece of redstone off to the side, unless you break the redstone on the transparent block and place it back again or if a block update happens right above the piece of redstone on the transparent block.