Hi Daniel, I think I have figured out what is happening and this is not new behavior to 2018, I see the same issue in 2017. We made improvement in this area in 2018 not to pass the z height of varying entities but the reason that LayOut is displaying dimensions like this is that the view is not parallel to the axis. When this occurs LayOut believes you want to dimension the actual dimension.
I noticed two things that tipped me off that this was what was happening.
First, LayOut dimensions should display rt angle marks on dimensions when dimensioning in parallel axis. Dimensioning the model and selecting the dimension did not produce these marks but a diagonal dimension.
The second thing I noticed was that the section plane appeared to display ‘double’ section marks on top of each other in LayOut.
I opened the model in SketchUp at the current scene “Front - SecCut5 - Sparge Outter” and verified that I was seeing double. :0)
I then zoomed out without obiting the view (middle mouse wheel scroll) and noticed that the a green axis was going diagonal even though the view was in parallel projection.
I turned on the Layer C - Section 5, entered the component, rt clicked on the active section plane and selected ‘Align View’. The section marks now displayed correctly and the axis displayed parallel.
I then Updated the Scene, Saved the file and Updated the model reference in LayOut.
The dimension will now display the correct distance and selecting it will display the rt angle mark.
Please let me know if you have any questions or need any additional clarity.