Hello,
Thank you for pointing it out to me! I forgot that the default template set Working Unit to 0 digit, that's why 0.1mm shows as 0 to me.
Regarding the double line, I tried again and found that the Tread's Finish Extension, by default, is set at 15mm. If you set it to 0, no double line should appear on the stair. I attached a screenshot of this parameter.
Hope this helps!
Best regards,
Minh
Minh Nguyen
Technical Support Engineer
GRAPHISOFT