If an admin sets a custom invoice numbering scheme it does not reflect in all sections of WHMCS.
The obvious one is if you generate a statement for a customer from the Admin Client Area it will show the internal invoice ID, but if you look in the invoice section for the customer it will display the custom names.
I have found the same behavior in the iOS app, if I have ticked the box saying that I want a custom invoice number scheme in all spots, it should not default back to the internal numbering scheme - they should all be the same.
I find it hard to believe anyone that is using WHMCS wants to see the internal numbering scheme if they have set a custom scheme.
Hoping that others have a need for the same functionality