PEdit from 2D Lines creates Plines with Random Elevations

[Anonymous]

Running C3D2017.  Empty drawing with some XREF's attached.  

Draw (trace) a building footprint using an XREF as a guide, using LINE command.  All line segments show with Z=0.

Attempt to PEDIT the line segments into one closed polyline.  First time through, no issues.  

Second outline - Prompted to make line into a pline.  Answered 'Y'.  Selected 'Join'.  Selected segments.  Enter.  "zero segments added".  Huh?

Checked original segment.  Now a polyline as expected, but with a random elevation.  Attempt to set elevation to 0 and segment disappears from drawing.

Attempt to create pline another way.  PEDIT, but select 'Multiple' at PEDIT command. Select all the lines.  Prompted to make plines.  "Y"!  "Join".  "Zero added".  Now all segments are plines, again with random elevations.  Some positive, some negative.  Attempting to change elevation via Properties again causes the selected line (or all lines if all selected together) to disappear.

I've restarted the computer, audited the drawing etc.  A clean drawing allows the lines to be joined into one pline as expected, but not in the drawing I need.  

I suspect an XREF is involved, but if so, I don't understand why I was able to draw the first outline successfully.  And I need the XREF to be there!

[LeafRiders · Accepted solution]

Regardless of the underlying issues you're having. If you know you can select just the lines you want to "Join" or "Pedit > Join", try running the FLATTEN command prior to Join or Pedit > Join... This will ensure all your segments are good to go. Good Luck!

[Anonymous]

Yes, thanks, that works.  Why FLATTEN will do it, but setting the elevation to zero in PROPERTIES won't, I don't know.  You'd think the process would be the same under the hood.

I'd still like to sort out the underlying problem though...