Changing the Python numbers makes no difference.
Very strange indeed.
To me it is looking like a resizing problem (I used some very odd image sizes for those dds files). I have only an old 17"crt display, very forgiving to any graphical artifacts. But if these lines are really there I should at least be able to notice them in screen caps. What picture format you are using for civ4 screenshots? Jpeg?

), meaning due to the rounding some pixels are "sort of there" (that's why 66.67% is a zoom that always looks terrible, whereas multiples of four (in zoom factor) always look "right", because it's a matter of chucking out every second pixel (x2), doing that twice (x4) etc. - can't do that for 2/3 properly). That's also the reason why .dds files must have sizes that are multiples of four - to make proper mipmaps.

