Cant set links to open in existing tab

I am using twenty thirteen

All my links are opening in new tabs because I set them to do that by clicking the box in the link settings.

Now I want to open some in the existing window tab but every time I unclick the box and update it returns to being ticked and opens in a new tab.

What am I doing wrong and how can I resolve
Thanks

• This topic was modified 8 years, 1 month ago by steve.warnes.