This was the topic of two separate tech support calls this week. If points make a line, two problems make a blog post.
First, I want to talk about the corridor section editor in general. It is an AMAZING, powerful tool. If you build a corridor and need to tweak the cross section at a station or a range of stations, this is how you do it. Some users attempt to modify the cross section views. The section views are only a reflection of the model and cannot be used to change your corridor in any way.
You will be taken into a purely data-driven view of your cross section.
Here's the rub - you *can* modify the section graphically, but you cannot mix graphic changes with numeric changes. If you went through and tweaked a lane width numerically then graphically edit the daylight line, the graphic edit blows away all your numeric changes. So...you need to decide how you are going to make the modifications and stick with it.
Ok - here's where I get to my original point: When you are done making your edits, save the drawing, then close the section editor using the ribbon! Even if you are done for the day and want to go home, close the section editor first.
Life will go back to normal...at least where Civil 3D is concerned.