Unsplitting Zpolylines without flattening vertical line segments?

Question

Trying to figure out how to fully keep vertical line segments when using Dissolve/unspit lines...

The first image shows the original Zlines in Arcscene

The second image is the result of a Dissolve /Unsplit lines

Vertical Segment (identical x, y but different z) are missing, the vertex are deleted and not simply stacked.

This is a known Problem (already identified with ArcGis10.0 but apparently unsolved) : http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002t00000010000000

Looking for some workaround, I found an earlier Q&A titled Vertical lines in a polygon shapefile. It could be one of the step of a larger process.

Has anyone had to deal with dissolving/unsplitting vertical Segment?

Using ArcGis Advanced 10.2 + full Version of Edit Tools, FME, QGIS (AutoCAD is available, though no expert user on site).

Answer 1

This is still documented as a Software Limit at ArcGIS 10.2.2 for Desktop:

Tools that aggregate and combine feature geometries, like Dissolve, may also flatten vertical line segments.

There is an existing ArcGIS Idea to have Support for absolutely vertical lines or line segments in Dissolve Tool added:

Lines with vertical segments (vertices have the same xy position but different z values) will wrong processed via the dissolve tool. Only one vertex will retain at the same position, therefore the geometric situation in the output is not corresponding to the input.

Irrespective of whether any workarounds are offered via other answers, I would recommend that you add your vote to the above.