When a logged-in user visits my forum, it looks like this:

As you can see, the user can't start a new discussion. This changes when he/she clicks on one of the tags:

That means people can post, but I'm sure there will be users who don't understand how to post. And since this setup is very similar to this Flarum forum, I know that this is not how it's supposed to be!
Here's how the tags are set up:

Is this wrong? I'd like people to always select one main tag (like "Starling") and one sub-tag (like "General").
To be honest, I'm somewhat confused by the difference between a sub-tag (i.e. anything that's hierarchically below a primary tag) and secondary tags. I know this setup says it requires exactly one secondary tag, even though there are none; but except for the issue about having to navigate "into" a primary tag before being able to post, this seems to do exactly what I want.
[BTW, I'm on the very latest version of Flarum (v1.1.1) and the only non-standard extension I installed is Byobu (private discussions). However, deactivating that doesn't make a difference.]
[And one more thing: admin users are not affected by this issue. They're always seeing the "Start Discussion" button.]
Any help is appreciated — thanks a lot in advance!