pdf file from DITA-OT output, the headings always comes with underline, why?

Using FrameMaker2015, I created a DITA 1.2 topic and create a document but whenever I generate a pdf file from DITA-OT output, the headings always comes with underline like this:

How to ignore those underlines? I tried all that I can in master page view, but couldn't ignore it. By the way, If I only save the doc in pdf mode, then underlines disappear. Please help by giving any clue. Thanks a lot in advance!!

Mehjabin

Any answer from anyone?