What I forgot, the feature can be disabled/enabled in "Settings -> Environment... -> View".
The first double-click creates a new perspective named "Code::Blocks minimal".
The default does not show anything, but the menubar and the editor panes, but it can be changed to fit the users needs, as any perspectives.
The second double-click returns to the previous perspective (if any).
If the perspective is totally messed up, the default can be recreated (as the default perspective) by deleting it (it will be recreated from scratch in this case).