Difference creates duplicates

[gruvw]

When using the Difference function, the result is two times the same shape in the output:

You then export to STL or STEP and when you import to a different program you actually get the shape twice (they are superposed but you see them when you click split to objects):

I expect the Difference function to only output one object.
Note this does not happen with Union or Intersection.

let box = Box(10, 10, 10, true)
let cyl = Cylinder(2.5, 10, true)

Difference(box, [cyl])