The default situation was that the toolbox grabbed the focus when clicked. That meant various actions, eg. "Show/hide docks", didn't work if the last thing you clicked was the toolbox. That's an annoyance created by "accepting the defaults", that's thankfully now been fixed in light of real-world usability issues.
https://git.gnome.org/browse/gimp/commit/?id=52ad5bb2a11e39f...
The default situation was that the toolbox grabbed the focus when clicked. That meant various actions, eg. "Show/hide docks", didn't work if the last thing you clicked was the toolbox. That's an annoyance created by "accepting the defaults", that's thankfully now been fixed in light of real-world usability issues.