During regression tests, I noticed that after trying to enter a user with an incorrect email address, this user is saved.
Log in as an administrator.
Go to Administration > Users.
Click "Add User".
Fill in the required fields (e.g. username: test3) and enter too short e-mail address : test@gmail.
Click the "Create User" button.
Click the "Close" button and then "Cancel".
Using the "Filter", search for the user you want to enter earlier (e.g. test3).
The user is on the list, but can't be edited.
The new user should not be created.