More feedback:

The 3D view turns all grey after:
- switching to SW3D window (after it was in background or minimised)
- resizing SW3D window
- hovering over menus

The 3D view return to normal when you drag the camera and force it to refresh.

Happens on both my machines (Win 7 x64, AMD Radeon 4870 & 5570)

Cheers