@roflmfaoo: I built the border images with 1px actual border and 2px shadow on the left and right borders because if I didn't do so Windows would not let windows resize horizontally anymore (the border wouldn't be recognized as such with the 1px border only, so Windows would never show the resize arrows). But the shadows are calculated to work fine:
As you can see in the image above, on the left there is the composed window when all parts are put together, in the center there is the parts mask (darker for borders, lighter for shadows), and on the right a semi-transparent parts mask over the composed window which clearly shows each part's boundaries. But you can clearly see the issue in my skin is not related to my sources at all. In fact, any window that doesn't use an extended glass border will use the correct border color. Only windows that extend the glass area will create this glitch, and the glitch is created just near the extended glass border. If my sources were using a wrong border color you would notice it in the image above. If I was using any wrong painting margins the borders would result in a much stretched and pixelated image but never in a more transparent border. In the window previews in SkinStudio and WindowBlinds you can clearly see the borders are painted correctly.
The point though is not whether this is a bug/glitch in WindowBlinds or SkinStudio, it's about how may I fix this? If you manage to fix it for me let me know,but I am trying since a few days now to rework all the sources in many ways with always the same result...
BTW, I am already using PNG 32-bit files in my sources, but SkinStudio converts them to TGA and I can do nothing about this.