The bug

The command block GUI button for toggling whether output is tracked uses X and O as text, which is also read by the narrator.
However, it is questionable how useful that actually is since X looking similar to a cross (for disabled) might not be obvious for a person with reduced vision.

How to reproduce

1. Enable the narrator in the accesibility options
2. Place a command block and right click it
3. Click on the button with the text O for toggling output tracking
   The narrator reads "track output X button"