Tabs content ads "—————-"

I’d like to get some support regarding one issue that I’m facing when I fill the “Tabs Content” section for each tab.

In concrete, I type the tab content in plain text (not html format), then I save, and I notice that this “—————-” is added to the end of every Tab Content section.

HAVE A LOOK

Just to add some information, I ‘ve seen the same problem here in the Demo, same lines at the end of the Tab Content:

http://paratheme.com/wp-content/uploads/2014/10/tabs-flat-active.png

Could you please give me a hand and tell me what am I doing wrong or how can I get this lines away?
Thanks!

https://wordpress.org/plugins/tabs/