I have been told that the Offset Line is getting added to the Sideslope "Container" and that is why when it gets updated the offset line gets removed. Can you create the Sidewalk Line by Offset / Elevation from the EOP line for now.
I am asking to be able to "Explode" a sideslope object to detach the dependency if you want to, because often I just want the linework as a starting point and I need to hack in Drop Curb or Curb Tapers etc and doing it all with Tables while possible is kind of hard work sometimes compared to just editing a Linestring by adding VPIs where you need them
The developers are thinking through this problem, but it will be next release before it is resolved.
Alan