The use of the square brackets to change brush size seems to be very haphazardly applied.
Currently (or at least last time I checked a few weeks back) they don’t work in Liquify, Develop or Tone Map but do work in Photo Persona but rather irritatingly stop working when you enter Refine Mask or Selection mode.
To me it is axiomatic that short cuts be as global as possible. Having them appear and disappear can get a little irritating when they work in one place and not another. The Ctrl-Alt click and drag in image to change brush size is global and works in all of the above. I really think this should apply to the bracket keys as well