Perhaps the title is rather verbose, but I am assuming that this is unintended. As a staff member (or a TL4 user), I can create topics as unlisted by default (rather than having to create the topic and then unlist it).
Since this is available prior to posting, I would imagine that the intended usage (when doing prior to topic creation) would perhaps be rough drafting, or having the opportunity to double-check markdown prior to public viewing. Perhaps an intended usage would be for the topic itself being intended to as direct-link–only.
To clarify on the bug: if a user has set their Preferences to give them automatic notifications for new topics created in a category, and staff then create a new topic (manually set to “unlisted” prior to posting), those users will receive a direct notification about the new topic being posted (and the “unlisted” aspect is nearly redundant, in some situations).
This is a minor (perhaps cosmetic, in some situations) inconvenience that can affect some users. Or, if a site has set default notification settings for certain categories (e.g., announcements, updates, events), then it can affect everyone who has an account and hasn’t chosen to change their default notification preferences.
If this is the intended functionality (that newly-created unlisted topics still send out “new topic” notifications), then my suggestion would be to have it not do that. While it would make sense to send out notifications for other things happening with the topic (e.g., replies, likes), I don’t think it makes sense for “new topic” notifications to be sent.
EDIT: It’s quite possible that this is intended and that instead of fulfilling my suggestion / bug report, that a more appropriate action would be to direct me to use the “shared drafts” functionality.
I don’t think that “shared drafts” cover every use-case for unlisted topics though, so perhaps I’m trying overthinking the functionality of unlisted topics and everything is functioning as intended. But if that’s the case, then it seems a bit “meh” to have the ability to toggle unlisted/listed prior to topic creation, besides for consistency, if it doesn’t offer any extended use-cases.