Why does Impress leave fiducial marks (dots) around polylines?

When I use the Polygon (or Multiline) tool to draw things like the red brackets in the screenshot, Impress (4.4.5) shows tiny extraneous dots (like fiducial marks) at low zoom (like 85%). They disappear at 100%. Is this a feature or a bug?
image:!(C:\Documents and Settings\Micro Center\Desktop\Fiducials.png)