SW 2009/SP 3.0:

I frequently get the arrows belonging to some assembly drawing balloons turning to dots.  I know I have placed them correctly touching the edge of a part, not a face.  Some operations later I discover what used to live as arrows have metamorphasized into dots, still located at the edge.

I'm not quite sure if every time this has occurred the leaders affected happened to have been to the leading balloon in a stacked balloon set.  But this is true of my last couple of assemblies.

Any ideas why or how to fix, anybody?