Opening a Style (Character or Paragraph) dialog's Font tab adds Asian text size (11) to the properties set in the style (visible on the Organizer tab).
The Asian text font size is 10,5 pt by default. When the Fonts tab is opened, the fractional font size is wrongly detected as modified wrt initial; so the property is added to the style. It's impossible to remove this setting from the style afterwards.
Mike Kaganski committed a patch related to this issue.
It has been pushed to "master":
tdf#115892: properly get the box' saved value
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.