It comes from being quoted in either the PHP or SQL content (or both). The characters ', ", etc... are all special characters to both PHP and MySQL so they must be "escaped" (that's your backslash character like \').
Now, depending on *when* exactly the escaping is happening, and the exact SQL insert command/options/maintenance scripts that run, the escaping could be happening multiple time, which will give you the double back slashes (one for the PHP, and one for the SQL -- \\\' -- You've gotta escape your escape character because it's a special character as well ya know)
One is normal for SQL text inserts, it gets unescaped by PHP after being pulled from the database.
More than likely, because of the CMS's hooks, the text is being escaped more than once in multiple modules, so you could have the text being escaped two-three times, which is just going to add backslashes .... 1 per backslash that exists (and if badly written, adding another to the ' character).
Cuz, well, each escape character must be escaped too ya know. Us computer people don't like doing easy things.
Edit: As a note, to *insert* the backslash characters to display as I wanted, I had to double them. The text gets unquoted before being processed.