I’m not sure if the cause is openSUSE, Chromium, or Virtualbox. I am running openSUSE 13.1 as a Virtualbox guest in Mac OS. I have installed Chromium.
The problem with Chromium is that the web page area within the application window always takes focus, even when Chromium is not the application with focus. Anything that is on top of the Chromium window is hidden under the web page area. The same goes for drop down menus within Chromium. I click the 3 bar button at the right side, and it is hidden behind the web page area.