I stumbled into a very much related issue, just that the behavior is even a little different to it being described here, but it’s also been a year.
The tl;dr is that admins are allowed to create invites whereby the invitee is added to one or more groups immediately as they create their accounts. Regular members who are group owners cannot.
If I am a non-admin group owner who’s been granted invitation rights, I can actually invite people with a link that I created (and that has a group parameter) onto the platform as well as into the (one) group in the same step?
My issue is, that the available link creation buttons on the group page have different results for which the creator receives no direct feedback, as described here. So I agree that this is more of a bug than a feature.
I see that there is also the invite option via the profile page and if I create a link there it will not have a group parameter. I expect this. But if I invite through the group page, I expect to invite into the group no matter what.