UV Unwrap at seams gives unexpected result I'm trying to learn UV unwrapping.

I've an object where I marked the seems. When I UV unwrap it, some (planar polygon) faces unwrap in an unexpected way:



It appears blender detects something that is not there.

What causes the distortion and how do I get rid of it?

Is this because I use polygons (all polygons are planar) instead of triangles?


Update
I posted the .blend file on blendexchange:
I unwrapped your model again and the other side also gave the same result. Then I tried Smart UV Project and all your shapes came out nicely. In conclusion I think you are better off doing the Smart UV Project instead of the standard Unwrap and as far as why the standard unwrap does this, I think it's because of the way Blender's default unwrap algorithm works.

Hope this helps