> Perhaps. But that doesn't explain why alt-tab when using '-video d3d' and running > full-screen works as expected (does switch between windows).
It's possible the front-end you are using, the card driver, any other program, an unfocused dialog box or the build itself you're using is generating a hidden window under those modes. When that usually happens pressing Alt twice fixes the problem (Hold Alt -> Press Tab twice -> Release Alt). Try three times if necessary and tell us what happens.