When text is copied into the listing from another program, it can sometimes bring formatting from the previous document which then overrides the website formatting.

1. Edit the listing
   
2. Go to the marketing details tab
   
3. Click into the listing description
   
4. Select all text in description
   
5. Cut the text out, then click in and backspace a few times to make sure you get all the text and formatting out
   
6. When you paste it back in make sure you only paste as plain text. 
   

Its best to use keyboard short cut functions below

Mac : Command+Shift+A

Windows: Ctrl+A

Paste as plain text on Windows - Ctr + Shift + V

Paste as plain text on Mac - press Option+Shift+Command+V to paste text without any formatting