Linked offset path always closed (open paths offsets should be like a equal-width powerstroke)

Migrated from https://bugs.launchpad.net/inkscape/+bug/170373

Steps to reproduce:

• open Inkscape
• draw a path
• apply "Path -> Linked Offset"

What happened?

• the resulting object assumes a closed path when it is not

What should have happened?

• the resulting object should look like and behave like a simple "Power Stroke" path effect with only one handle

Inkscape Version and Operating System:

• Inkscape Version: 1.0alpha (1:0.92.0+devel+201904112206+331007d)
• Operating System: Ubuntu
• Operating System version: 18.10

linked-path