[Pro Sites] Passwords for newly issued sites don't work

When a new user creates a site (paid or free) the password sent in the welcome email doesn't work. The user must do a password reset to get a working password.

This is similar to this ticket:

https://premium.wpmudev.org/forums/topic/wordpress-pro-sites-newly-created-users-wrong-password

The difference is that I do not have the Manual Payment gateway enabled. Free sites are affected, so payment gateways are not involved.

Support access is enabled.