Hi
All glyphs move after adding x-Height and need to update metrics.
before adding x-Height in Master Metrics:
after:
when i delete x-Height, glyphs with update metrics going back to their previous location.
The glyphs doesn’t move. Only the bounding box does. The slant is computed on the half x-height. This will lead to more even sidebearings and better fitting with upright text in the same line.
oh, OK. i understand this is a feature now and my next question is a disappointment, but is there a way to disable it? 
Why do you like to disable it?
In the next version (3.2) you can manually overwrite the slant height by adding a custom metrics with that name.
because all of my side bearing calculations are based on the primary values… OK, I’ll wait for 3.2. thank you :))
You could “fix” the sidebearings by moving all glyphs 57 units to the left with “Paths > Transformations”.
Try to type a few “nnn” in Indesign (or any app). then set each second one to be italic. You will see that the italic lean into the next upright n.
It’s just fix the numbers, glyphs actually move and maybe cut from one side in some UI. (it’s not a big deal now that i understand).