Well, basically the problem with mapping is that must be applied before Segments are deformed (Bend, Slice, Clipping, etc.). If not, in many cases the result is not correct.
But on the other hand, capping must be applied after those deformations, because the open polygons are generated mainly by the Slice and Clipping processes.
Unfortunately, the "Cap" Max function messes up the mapping coordinates. With standard objects this problem is solved reapplying a UVW Map modifier, but we cannot do that in RailClone because the reasons described above.
Sorry if i didn't explain well the problem... these concepts are a bit tricky to describe by words.