Open page in new tab, not working

When I am writing or editing an instructables I usually put in some links, when entering the link I get a option to "Open page in new tab", The only issue is that when I enable and save that option the link opens in the same page and then the box is unticked when editing it again.

I have included a short video about this Here https://youtu.be/OHCSXtDeIkk

MacBook Air (Mid 2013)
MacOS 10.12.3 (Beta 16D17a)
1.3GHz i5 2 cores with hypertreading
4GB 1600 MHz DDR3
Intel HD Graphics 5000

Safari 10.0.3 (12602.4.3)