The docs on Managing multiple directories describe this sample scenario:
- You have connected two directories: A read/write LDAP directory and the internal directory.
- The LDAP directory is first in the directory order.
- All new users will be added to the LDAP directory. It is not possible to add a new user to the internal directory.
If that's true, why can I perform the following actions?
With this directory order:

I select 'JIRA Internal Directory':

And the user is created in JIRA Internal Directory:

So the question is: Why am I able to create a user in JIRA Internal Directory?
My guess is that the configuration of the LDAP directory might not be read/write, but I am unsure on how to check that, even after having had a quick look at the 'Directory Configuration Summary' page.
Any ideas?