Same stairs - different beyond cut line

[barbara.ivo557941]

Somebody help me understand this please:

(look at the jpeg): I have a group that contains one circle spiral stair (2.8m height), one railing and one pilar for the stair. I mirror it as I need. My plan view, obviously, has only a 1.7m cut plane in the view range (I'm not using plan regions).

How on Earth these two exactly equal stairs (the same group!) shows different numbers of treads beyond the cut line?

Help, please?

[Brian Myers]

Are they at the same elevation? I know they should be, but verify that they are... I'd bet there is a difference.

[barbara.ivo557941]

Brian, this time, unlike others, I checked those obvious reasons...
Look at the section: exactly the same heigth.
What am I missing?