So my question is; Is that the way it works? Or should it query AD when I click on the Customer page automatically and show me everything without having to perform a wildcard search?

That's the way it works. Why do you want to see a list of customers anyway? It could be pretty big.

CustomerUserSearchFields => ['sAMAccountName', 'cn', 'mail'],

If you add 'sn' and 'phone' to this list, you can also do searches on last names and phone numbers when trying to pick a customer for a new phone ticket. -- Lars