Which is entirely the purpose of the category change notifications delivered to that user.
Non-issue, as if you are tracking or have otherwise participated in the topic, your notifications for the topic will continue as usual. They are completely unaffected by the category change.
Why? Just to grief everyone else in the feature category? What purpose does it serve to keep a duplicate link there, to a topic that doesn’t even belong in the feature category in the first place?
If you are ignoring notifications, how exactly did you find out I posted this reply to you? To argue that users will ignore notifications, well, users might opt to turn their computers off and go live in a cave, too. Or just quit the forum for reasons. That’s possible. But is it likely?
Bear in mind, too, that recategorizing a Discourse topic does not change its URL, because URLs to topics do not include the category. So if for some reason you had old-school bookmarked the URL to the topic, rather than just relying on the automatic tracking (you created it, you replied, etc) and read time tracking (you read it for more then 4 minutes) you’d be able to get back to that topic from the same URL no matter how many times it is “moved” from one category to another.
I feel very strongly this “shadow topic” feature is due to weaknesses of old forum software design, e.g. they had no practical notification system when recategorizations occurred, and/or their URLs were affected by category, so they had to spam everyone on the site with these shadow links as a result.
Personally, I’m not a fan of spamming everyone due to deficiencies in old software. Everyone who would care about that topic either is notified directly, or doesn’t care because everything just keeps working as you’d expect.