Talk page preview on message pages creates "Changes you made may not be saved" window in browsers
When creating new topic on e.g. https://translatewiki.net/wiki/Template_talk:PLURAL, after typing something and clicking "Show preview", I get Leave–Stay window (in Chrome: "Changes you made may not be saved."). Same happens when saving or leaving talk page after saving.
Also, after I saved this thread / new topic here on Support and tried to leave page, I got Leave–Stay window (after choosing to Leave, message was saved indeed – so conclusion is that something is 'false-positive' creating this). Editing this comment is fine, no Leave–Stay window.