Hi, ragnar.

Just to expand on what Miss Nancy said, Poser's magnets work by affecting the existing vertices of the underlying geometry. They can't (directly) affect edges.
Switch to a wireframe view to see the way the object (or part of it) is made up. Vertices show up as the "points" where lines (edges) meet.
Lines (edges) cannot be affected by magnets, only the vertices (points) where they join are affected.

Hope that helps (and that I'm not telling you anything you already know)

Cheers,
Diolma