Now I have examined this a bit and I have found out:
Line types are always printed out the same on paper (or to pdf), regardless of scale and units, just as is the case with line widths.
But the rendering on the screen is wrong, unreliable. I don't know if this can be fixed, I'm not a developer. Nor do I know if this worked right in an earlier version.
As a workaround I have made an A4 sheet with all the line types in 0.25 mm and 0.5 mm you may use as a reference.
linetypes_mm_1_1_a4.dxflinetypes.pdf
Maybe there are certain conditions in drawing mode or print preview where it looks approximately like when printed, I have not found out yet. Perhaps you will discover that.