bone rotation plus/minus gives the same movement

See added file game_bucket.blend (958 KB) for setup.

I am trying to control a rig with user input. One bone works fine (keys W and S) but the other control (keys Q and A) gives the same movement, even though one key adds to rotation and the other subtracts.

In addition to this, the rotation seems to behave vastly different depending on what position the bone has. What am I doing wrong here?

UPDATE: The effect disappears (So, it’s a temporary solution) if I turn on “inherit rotation” on the problematic bone. This behavior, however, is not apparent from moving it manually. What gives?