Steps to Reproduce:

1. Create any user on JIRA (e.g. test@atlassian.com)
2. Create another user on JIRA (e.g. test@jira.com)

Expected Results:
There is no documentation about it. But I suggest the system to create the user with something like 'test1' when the username already exists.

Actual Results:
The system is creating a 'random' username. E.g.: u15

Notes:
Since customers lost their ability on managing usernames, they are already complaining that this behavior impacts mainly companies that are audited or are supposed follow governance processes (like Sarbanes–Oxley, COBIT, etc).

Also, customers'd like to have the ability to manually set the user's properties when creating them.