If trying to move an attachment from a particular page to another page which already has an attachment with the same name, an error message is generated "This file name already exists in the destination page".
This is not consistent with the behaviour exhibited upon uploading an attachment with a duplicate name from the same page. In this case, the duplicate is saved as the latest version and the previous document is marked as "Version 1". No warning/error is generated indicating a duplicate or an overwrite message.
The same behaviour is expected while moving an attachment from another page.