Adding Circular or Chromosomal glyphs has inconsistent new backbone behavior

[travisformayor]

Clicking a Circular or Chromosomal backbone glyph when nothing is selected adds a new backbone, but when a backbone is already selected nothing happens. Dragging a Circular or Chromosomal glyph onto the canvas with nothing selected does not create a new backbone if there is an existing backbone already, instead selecting the existing one, and only creating a new backbone when the canvas is completely empty.