Comment 3 for bug 1758536

Seems to be related to Tavmjong's latest attempts to support the path "d" property (i.e. the actual path data) as a CSS style attribute.

To fix in your preferences.xml simply delete the unwanted styles from the entry
  <group id="desktop" style="...">

You might want to ping Tavmjong, though, if this gets always added when using the master branch (we wouldn't want to store arbitrary path data as a "default style")