Opening a Style (Character or Paragraph) dialog's Borders tab adds Shadow properties to the property set in the style (visible on the Organizer tab).
The shadow size is 100 twips by default. When the Borders tab is opened, the shadow size is shown as 0,18 cm; then on reading back, this arrives as 102 twips, and wrongly detected as modified wrt initial; so the properties are added to the style. It's impossible to remove these settings from the style afterwards.
Mike Kaganski committed a patch related to this issue.
It has been pushed to "master":
tdf#115938: Properly detect shadow size control's changed state
It will be available in 6.1.0.
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.