This is actually a bug in the platform that I noticed earlier this year.
The platform has a before Commit event on System.User, this BCo microflow does the follow:
- database retrieve and (aggregate) count the nr of System.User entities
- split users count > max allowed users
- If true, prevent the commit and show and error message to the user
- If false allow to commit.
As you might be able to recognize, this is broken for two reason it performs a > check while the license does a >= check, and there is a db retrieve in a before commit which won't find the user that is being created.
In the Mendix 6 version I tested with (I thought 6.4) I was able to get user feedback when I was creating 2 users more than maximum. But at re-start I would still have a problem.
I've been told that this is fixed in 6.5 (through ticket: 40085) and the platform should prevent you from creating a user through the UI when you reach the maximum. (I haven't tested this since submitting the ticket). So please if you can still create too many users in 6.5+ submit a ticket for that.
You still can create new users. Problem is that no one is able to log into your app. Not the most userfriendly behaviour. We had a couple of times clients going over their license limit with the result that nobody could log in. The MxAdmin had to deactivate users first so users could use the app again.