Problem with kwin decoration windows arc-dark with virtualbox

[vincenzogianfelice]

kwin_error_arc_virtualbox.txt

Hi. I noticed that when I set the theme of windows with "arc-dark" and try to set up configurations, in particular the USB controller, it locks both virtualbox and kwin (the window manager of kde).
With the theme of "standard" windows this does not happen.

Thank you and sorry for my english.