Empty lines are not handled correctly

Follow this steps to reproduce:

• Edit a new page
• Switch to Source and set the content to:

  before
  
  
  after
  

  (the two empty lines are important)

• Switch to WYSIWYG. First problem: the line between "before" and "after" is not styled like a paragraph (there's not enough spacing between the empty line and the "after" line)
• Switch back to Source. The source is now:

  one1
  
   
  
  
  two
  

  Second problem: two more empty lines have been added and one of the empty lines contains a space character.