Created attachment 1496687 [details]
logs and screenshots

Description of problem:

When a new user is created in CFME UI, logging in as the created user in some cases fails with 500 Internal Server Error.

Data {"error":{"kind":"internal_server_error","message":"Invalid userid uidzzj5dmgyuv specified","klass":"RuntimeError"}} 

From what I tried, the issue doesn't depend solely on username length or combination of alphanumerical characters. With generated username in the following format:
user_[a-zA-Z0-9] in total 13 chars long it happens every time.

As can also be observed in the screenshot, the user has a Last Logon timestamp, so the problem is not wrong username/password.

Documentations provides an example for creating a user with username 'my_user', which works along with usernames like 'test' or. '01234567891'.

These usernames lead to the error:
user_487UIXkKM2, user_bOVmgFk5d2, user_e8EpvBRg5z, user_e8EpvBRg5z

Version-Release number of selected component (if applicable):
Version 5.9.5.2.20181015201954_5f1530c

How reproducible:
always with generated username in format 'user_[a-zA-Z0-9]'  

Steps to Reproduce:
1. Create a user with username user_[a-zA-Z0-9], for example user_bOVmgFk5d2
2. Try to log in as the user

Actual results:
error 500

Expected results:
successful login

Additional info: