When setting link properties in the editor using the Link Properties button, if you use the Target drop-down menu to set where the link will open, then edit the properties of another link, the Target drop-down menu shows the selection from last time the window was opened, but when you save, the link target is NOT set.
For instance, if you set a link target to : "New Window", it correctly adds target="_blank" to the link. If you then select another link and click the link properties button, the Target drop-down menu still shows "New Window", but when you click OK, no target is specified. To set a target, the target drop-down menu has to be changed to a different value, and then set back to the desired value in order for it to properly update the link in the document.
I've recorded a video so you can visually see the issue that we're experiencing.
Ironically I'm able to reproduce this same issue using your editor here on your forums page.
Please let me know what change we can make to correct this behavior.