Unwrap without skew

I don’t know what is going on. This mesh gets its UV layout rotated in UV editor. Of course, I can rotate it back manually, but honestly, I expected getting orthogonal UVs, while the edges of my mesh are perfectly orthogonal.
It isn’t always like that. Sometimes Blender gets the UV rotation right out of the box, and I’m wondering where the difference lies.
I think I did the seams right.

unwrap.blend (2.1 MB)

hello, see my answer here: https://blender.stackexchange.com/questions/242207/how-to-fix-skewed-unwrapping/242209#242209

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Okay, I will do that, thank you!
I just kinda hoped that Blender can do it automatically, but it seems like we have a bug here.