I have noticed that this will happen regardless of whether the poster is allowed to mention the group or not, and whether the group is visible to all users or not.
I think that at least when the group isn’t visible, it should not link, because in that case it is just a dead link. And in most cases where the group isn’t visible, no one is allowed to mention or message it either, so if the @group link starts floating around, people may become confused about why no one responds to their mentions or why they can’t message the group. Perhaps there could be added a warning if a user tries to mention a group they aren’t allowed?
While testing this, I also came across a peculiar error when trying to send a message to a group I wasn’t allowed to message. I received the error
To do this, I started a message, filled in the message title, then used the autofill mention to mention the group in the body, and then using the autofill mention to add the group as a recipient.
On my main user (admin), it didn’t work until after a few tries. On the other users it worked immediately.
I tried this for two groups. Both groups were set to allow nobody to message them, but were visible to all users. I tried it on every trust level, as a moderator and as an admin, all across different users. I tried it across multiple browsers and devices, both mobile and desktop. But I only tested it on https://eve.community/.