Why scale affects animation rotation?

This is a box rigged with 1 bone and simple animation. The smaller one animates correctly, doing 30 degrees rotation. The bigger one is scaled on Z by 2 (1,1,2 scale) and as you can see, it rotates only half a way in the animation. The animation is the same.
On the right you can see skeletal meshes without animation, rotated by 30 degrees and looking just like it should look.

How can I make this bigger box rotate the same amount as smaller one?

I’ve just made an animation inside UE to make sure that’s not this specific animation what causes that. And results are the same: http://gph.is/1WG9fRi

Update: It’s certainly not a problem with my mesh, because any skeletal mesh (even these from Content Examples) behaves the same. I have no idea what’s going on here, is it somehow intended or it’s a bug? I haven’t checked in previous versions (4.10 now) yet…

Not sure of the solution. It looks like it’s adding a shear transform. Searching that brings some interesting results.

There has to be a way around this.

Does a uniform scale work?