Problem with Extracting Dynamic Feature lines from Corridors

[losfotos]

So I have a very simple corridor that has a curb and attached sidewalk and I want want to extract the feature lines for the lip, flowline, top face of curb, top back of curb and back of walk. I have 2 curves and a tangent on the alignment. The vertical alignment whoop de doo's the whole way. What is happening is that along the curves the featureline matches the corridor perfectly. BUT, along the tangent line it goes straight from one end to the other ignoring the vertical differences.

Any ideas on what/why it is doing this?