By using "Discuss on talk page" the page gets unwatched.
Normally the status of the "Watch this page"-checkbox depends on, if the page is currently watched or not. If you use the function, the checkbox is always unchecked, resulting in unwatching the page if not modified before submitting.

I mark this bug as major as I think that most users using this function already watching the article and so they will silently unwatching it.

Version: master
Severity: major