Why does entity snap mode “parallel” provide a dotted guide line only when working parallel to a line entity?

When working parallel to a line entity, entity snap mode “parallel” provides a dotted guide line as expected.

That guide line does not appear as expected when working parallel to a polyline.

Help notes suggest that it should appear with all “linear entities”.

My current work-around is to draw a line on top of the polyline and then erase it after setting up the parallel but this seems to be extra, un-necessary work.

[User of DS (Free) V1R3.1 x64 on Windows 7/64 Home Premium.]
25 Feb 2013, 19:42 (NZ standard time)