Updated link Target field is not updating when updating to certian values.

[JoeK]

1. Open the Link dialog.
2. Enter a URL.
3. Go to the Target tab and set the Target field to "New Window".
4. Click OK to save and close the dialog.
5. Select the link in the editor and open the Link dialog to edit the link.
6. Go to the Target tab and update the Target field to "<not set>".
7. Click OK to save and close the dialog.

Expected result:
The Target field has been updated to "<not set>".

Actual result:
Open the link dialog and goto the Target tab. Observe that the Target field remains set to "New Window".

This only occurs for specific combinations of original and updated values. See the attached file for test cases.

[JoeK]

Test cases that produce non-updating of Link dialog Target field.

[garry.yao]

Fixed with [4527].