Strange rendering bug, please help me debug it :(

I have spend last 2 days trying to use MyGUI library in my OpenGL 4.2 project.

Their samples were creating a win32 window in the sample code so I had to take quite a bit of stuff out.

The problem I have is when I call MyGUI::Render it takes the stuff that was rendered previously in the backbuffer and somehow moves it to the upper right hand corner of the screen (lower left corner positioned in the centre of my screen).

If I call MyGUI::Render just once and turn it off, my rendering from then on still ends up messed up :S

Can someone who knows OpenGL pretty well tell me what kind of function call could possibly offset my entire rendering to the upper right corner of the screen?

I checked viewport, its fine,
there is a GL_SCISSOR_BOX box active but that is just (0, 0, 1920, 1200) which is my res.