I've built a site on v2.3.7 and there is an issue with adding 'Open link in a new window?' to links when linking to an external page. I highlight the text, add the link URL and click the checkbox for opening in a new window and as soon as I click "insert Link' it disappears.
This is getting weirder. Internal linking is fine, but when I try to link to an external site (even without opening in a new window) the highlighted text gets duplicated and pushed to the start of the first paragraph.