UV mapping- and transparency problems

I created a texture in Gimp which has parts that are transparent. When I map it to an object in Blender, the following problems occur:

  • When I open the image in the uv image editor sometimes the image is not being shown in the editor until I move a Vertex. Is this a refresh bug?

  • The image is being shown upside down on the object. Of course I can just turn the unwrapped part in the editor by 180°. But I don’t think this should be necessary. Is this my or Blender’s fault?

  • Some parts of the exclamation mark and the lightning are way too light. Does anybody know why this happens and how to fix it?

  • For testing purposes I created another image in Gimp which is a gradient that goes from transparent (left) to opaque (right). When I map this image to an object in Blender the very left part shows an ugly stripe (2nd screenshot).

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The only thing I further found out is that I have problems with any kind of textures with transparent backgrounds. Let’s say I just have a simple line with a transparent background and I map it to an ordinary cube then the border of the line is brightly white.

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Its upside down because you’ve uv unwrapped it upside down.
For the white outline try selecting premultiplied in the render / shading / alpha settings instead of the default Sky

Indeed! Premultiplied solves the problem, but in the Texture / Image panel.
Thank you!