Stairway Specs Dialog Box Trouble

[Dekade]

When I manually change the number of treads from 11 to 12 (in the Staircase Specifications dialog box) the 'length' of the stairs will not stay at 111-3/4". The length changes to 122-1/4".

There are 13 risers and the top step (13th tread) is actually the first floor.

The height from the basement floor to the first floor - all inclusive - is showing as 102-3/8" in the Room Specification dialog box for the basement.

The Tread Width box is greyed out and stays steady at 10-3/16". I cannot change that or the riser heights.

How do I get manual access to stairway specifications?

Thanks