Symptom
===

when "Handle display brightness keys" is turned on:
1. press brightness-up: nothing happens
2. press brightness-down: brightness decreased

when "Handle display brightness keys" is turned off:
3. press brightness-up: nothing happens
4. press brightness-down: a notification pops up showing the current brightness level, which is not decreased

brightness-up/-down is CURRENTLY not in the custom key bindings.

Background
===

This happens after a whole bunch of pacman updates, including the ones of kernel and of manjaro.

Before the update, I used to turn off the "Handle display brightness keys" and to bind the brightness-up/-down keys, as well as the ones with Shift+, to custom commands of "xbacklight" for finer control.

After the update, the (shift+)brightness-up still works as usual, but (shift+)brightness-down no longer adjusts the brightness level. It only gives a notification showing the current brightness level, as the symptom (4) described before.

Then I removed all the custom key bindings of (shift+)brightness-up/down but the problem get reversed (brightness-up does nothing and brightness-down works) which indicates another layer of messing up instead of reduction of problems, and hence the bug report.