If I create a rectangular wire with four points and four edges, there seems to be two phantom lines that hilight the wire when passed over. These phantom lines seem to be view orientation dependent. It could be that I'm just doing something wrong. I don't know.
I've attached a small Linux/Qt4 example that shows the problem. The initial view displays the wire and two deactivated reference points that indicate the end points of the vertical phantom lines (in that initial view orientation).
I saw an earlier thread that mentioned the Y axis being off in hilighting, but I don't think this is the same problem. It's almost like the phantom line is part of a bounding box, but not quite.