Docks refuse to allow window to shrink vertically in single-window mode
This is quite significant. On my low DPI screen, GIMP (git master) docks seem to have a minimum size way beyond what they should be. My screen is 1366×768, and GIMP literally won't fit on it. As you can see by the GIF below, the toolbox on the left and the dock on the right have plenty of room to shrink but won't do so.