When not disabling Joomla's emails sending on new account creation in admin area, and creating a user without filling-in the password field, both Joomla and CB generate a random password of 8 characters.
Joomla email is sent first with a first password (that does not work) CB email is sent second with a second different[13.32:17 h] Nicholas G. Antimisiaris: At best it is a joomla bug password (that works).
We should either/or, better, do both of them:
1. use Joomla's password 2. avoid Joomla sending its email when a user is created in CB User Management (preferably not touching the Joomla setting)
Specially that an 8-character password is a bit weak, and that I will suggest in JSST to have 12-char random passwords instead in a future release.