For some reason, when a certain part I have is dropped into a drawing, some of its edges go missing.  When the view is placed, the edges are all visible, but after about 2 seconds, some of the edges go away.  I've attached an image to show an example.  The top/left view is the one with the missing edges and the bottom/right view is one that shows basically how it should look (it's a slightly different model).

Any idea why some edges might disappear?