Salesforce has an interesting limitation when it comes to cloning records. When you clone a record, fields that are not displayed on the page layout of that record are not cloned. So, since Soapbox Mailer's Edit HTML Body page and the Edit Text Body page are not fields that are displayed on the page layout of the Soapbox Mailer Campaign record, they aren’t cloned when you clone a Soapbox Mailer Campaign record.
A short-term fix for this is to do the following:
1) Go to Setup > Customize > Campaigns > Page Layouts: and click the Edit link for the Soapbox Mailer Campaign Layout.
2) On the Soapbox Mailer Campaign layout page, add a new section to the page layout, and call it whatever you'd like (maybe call it "Body Content")
3) Add the Email Body HTML and the Email Body Text fields into the newly added section.
4) Click the Save button.
5) Go to a Soapbox Mailer Campaign record.
6) When looking at a Soapbox Mailer Campaign record, click the triangle next to the section header you just created, thereby hiding the contents of that section (the two fields) from the standard view.
Now, when you clone a Soapbox Mailer Campaign, the HTML Body and Text Body fields will be cloned as well. In the long-term, we’ll see if there’s anything that can be done to move that data to a cloned Campaign record without needing to do the work-around above.