GUIs broken in Debian Jessie

After an update recently, I noticed that some GUIs were broken.

Astute readers may recognise that all the broken GUIs use QT (KeePassX, Skype and VirtualBox).

The solution I found was to install qt4-qtconfig and change the GUI Style from Desktop Settings (Default) to GTK+.

Here are the same applications after the fix:

VLC was also affected, but curiously undoing the change did not break the GUI again as it did with the applications in the screenshot.