xna - Strange rendering issue with monogame/WinGL with HD7670M

I'm having some strange rendering issues with latest monogame/winGL code as seen below;

As you can see the xna and tomspilmans WinDX port seems just okay.

I'm having this problem on my laptop with a HD7670M and it doesn't exists on desktops (got a 7970 and 5970).

Any ideas on the issue?