Cubase window loses focus on Windows 7

Hi there,

Since I upgraded to 8.0.20 I’m facing a really weird issue.
When I open a menu, say, the “Import Audio” menu to choose a sample, as soon as I click “OK”, Cubase Window get behind whatever other program is opened (Google Chrome, email client).
It also happens with other menus.

Have a look to this short video : HERE

My graphic card drivers are up to date and I installed the latest version of C++ as well. I have no idea why this happens…

Thanks for your advices if you have any