Graphics Analyzer wrong overdraw?

Hi,

Can anything make Graphics Analyzer to report wrong overdraws? I ask because my scene has one draw call of a rather simple geometry causing the overdraw to jump from 0 to 8 on the output pixels. Back face culling is on. I can't think of anything else that would make it have such a huge jump. Is there any GL state that I should be wary about? I am hovering the mouse pointer over the output pixels and the histogram also show a large amount of 8x overdraw pixels.

Thanks,

Denis