I had the same problem, but I found a solution, or at least a workaround. I exploded the polylines into plain lines. Surprisingly the lines didn't disappear, and the Z-coordinate of the lines were all at 0. Then I was able to trim the lines. So the ploylines had an elevation, but the lines didn't.
Log into access your profile, ask and answer questions, share ideas and more. Haven't signed up yet? Register