Looking at the code: the window of Konfigurator was supposed to be modal. I'll attach a patch.
But here comes a question: Would it be better if the Disk Usage window was modal?
The Disk Usage tool is available, for example, clicking in the
Tool > Disk Usage tool
menu and then clicking the OK button. But nowadays there are problems when minimizing the Disk Usage window.
If the Disk Usage window was modal, a simple setWindowModality(Qt::WindowModal); would solve the current situation.
But if the Disk Usage window is not modal, like nowadays, then one solution would have to be given to the problem of minimizing the Disk Usage window, because then that window is no longer seen, not even in the taskbar; until the user does something not intuitive like e.g. minimizing the main window of Krusader and later maximizing it.