Using Atto,

• I insert an image
• select the inserted image
• push the atto button "link"
• after inserting the URL (even accepting the auto-compiled description)

the image disappears and is substituted by the link description.

This can be tested also on current moodle.org forums.

If I insert a link, then in the <a></a> payload I add an image, it works.

I don't know if it's a feature or a bug .