[Bug] Closing or navigating away from new issue page doesn't warn user about "unsaved changes"

Normally when you’re filling in a form on the web and you try to navigate away from the page it’ll warn you that your inputs may be lost if you navigate away or close the page (using onbeforeunload). The new issue page doesn’t seem to do that?

After typing a fairly long and detailed issue, I switched to preview and then mindlessly clicked a link in the preview text. I lost all the text and had to start again.

Interestingly, if I click a github.com or google.com link in the preview, then when I click the back button the issue text that I inputted will still be there, but if I click a twitter.com link (to a specific tweet) in the preview text, then the body content is lost, but the title text is preserved. I have no idea what’s causing that, but it wouldn’t really matter anyway if I were warned about exiting the page when I haven’t finished submitting the issue text.