Link Text not editable when editing a link to an attachment

When you select edit on an existing attachment link using the Editor Property Panel the Link Text field is uneditable in the Insert Link dialogue box. If you are editing a link via the Editor Properties Panel you should be able to change the Link Text.

Steps to reproduce:

1. Edit a Page
2. Select Insert -> Attachment -> Choose File
3. Upload a file and enter some link text
4. Click Save
5. Click on the inserted attachment link in the Editor and select Edit from the Property Panel
6. The Link Text field is uneditable and you are unable to change the Link Text

To then be able to change the link text you have to delete the link to the attachment, select insert attachment again, search for the file you've already uploaded and then you can enter the revised link text. Which is a bit of a kludge.