What is causing formatting to break? We are using WYSIWYG with CKEditor on Drupal 7.

When the edit button on a node is clicked, the edit page shows text in a jumbled mess, even if there was careful formatting. The text formats have the "Convert line breaks into HTML" filter enabled,  as well as having the &lt;p&gt; and &lt;br&gt; tags allowed.  As per a comment, I have taken these tags out of the allowed HTML on the filtered HTML format.

WYSIWYG Linebreaks is enabled as well, but doesn't seem to solve the issue.

If breaks are added in, they seem to stay, even when editing the text again.

My question is: What is causing this formatting to break, upon clicking the edit button?

Example of ruined formatting:


On the left is what you see when viewing the page before it has been edited (i.e. the page was written by someone else), and on the right is the jumbled mess that is the edit page. On the edit page, all the paragraph or line breaks have been removed.
You are using using filtered html (Text Format).   [As per your screenshot above]

Filtered HTML only all the following HTML tags


Web page addresses and e-mail addresses turn into links automatically.
Allowed HTML tags: &lt;a&gt; &lt;em&gt; &lt;strong&gt; &lt;cite&gt; &lt;blockquote&gt; &lt;code&gt; &lt;ul&gt; &lt;ol&gt; &lt;li&gt; &lt;dl&gt; &lt;dt&gt; &lt;dd&gt;
Lines and paragraphs break automatically.



  You need to change text format to FULL HTML if you wish to retain all HTML formatting


As a best practice Full HTML use should be limited