The dockable should close as soon as it lost focus (unless you pressed the little “stay open” button on the title). It has the focus because you dragged it. Adding a “CDockableStateListener” to the Dockables (or the CControl) and focus some other Dockable once the “minimized” method is called, should help.
There is no property to change the behavior, that’s perhaps something for the todo list as well.