Steps to reproduce:
1. from a relationship editor, search for an artist, and use the "add new artist" entry in the results pane
2. put anything in the add link textbox (except something that would be auto-cleaned-up as a known URL type)
=> there will be a red error message, and the "enter edit" button is disabled
3. use the red X to remove the bad link

Result: "enter edit" remains disabled

Workaround: add a valid url and select a url type (reenables the button) and then click the red X to remove it.