If a repeating command blocks output connects to a redstone comparator, the command block being "always active", the comparator will light up when the command block has run a command successfully.

Then, if the command block is right clicked and changed to "needs redstone" and "done" is clicked, the comparator will still be lit up.

The expected outcome is that the redstone signal goes low.

If the command block is right clicked yet another time, and only "done" is clicked, the comparator will be unlit.

Technical description: The command block GUI will update the command output when the GUI is updated (as a result of the tile entity update), but not when the button "done" is pressed.