by John Okely.
The only way moodle would add an account early is when the synchronisation scheduled task runs. This was added in MDL-46623 for 3.0 so it would make sense if this was causing your problem. But before we know for certain:
Do you know if the scheduled task is running? Go to Site administration ▶︎ Server▶︎ Scheduled tasks and look for LDAP users sync job (\auth_ldap\task\sync_task). If it says "Task disabled" then it's not running. If it says the next run time or ASAP, then it is running and you might need to turn it off or reconsider how you want the synchronisation to work.
You could set the sync for email to on login to solve this problem. Unless there's a particular reason you don't want to?
Interested to hear more about how you want it to behave in an ideal world so I can suggest solutions