Steps to replicate:
1. Login in to admin panel and create an article
2.In article section , you have teaser, first paragraph and body
3.Add paragraph to those fields
4.Select a paragraph and click Bold
5.Check the updated styling
6.Select same paragraph and unbold
7.This does not work.
8. You can bold and unbold word in paragraph
9. Select paragraph and click Bold, italics and underline
10.Check the updated styling
11.Now again select paragraph and try unbold, unitalics and no underline.
12.This does not work
13.This works when user select a word and select unbold, unitalics and no underline.
14.Please check the video link http://www.screencast.com/t/czFDIjxIJ0hh for more details

Expected Result:

Editor should be able to bold/unbold,italics/unitalics and underline/no underline both paragraph and word.