[Leica] What causeth diaphragm-shaped lights?

["Richard J. Wyble" <rwyble@erols.com>]

Couple of weeks ago sitting in a restaurant at a window table taking
pictures of my grandaughter, using available light from the window, my
back to the window, the little darling across the table from me, dark
restaurant interior in the background. Some small low-level "mood"
lights are included in several frames and show up on film as
diaphragm-shaped sources of light.

The lens is a new Summicron-M 50mm and has a new Leica UV filter over
it, all quite clean. What's likely causing the distortion? Reflection of
the light off the back of that filter? Or something else?

  rwyble@erols.com                  Worcester, Massachusetts
  Richard J. Wyble