I think technically, it works as designed.
If you specify no [state presentation] then you get the default.
When there are no linked channels, you usually get a default string - though that can depend on the UI.
But if you link a channel, the binding can interact with the default [presentation]. The binding may look for units that you have chosen, or may supply formatting of its own based on an associated device perhaps. Where the binding can have no idea about the characteristics of a device (as with generic MQTT) then might get null default [presentation].
The summary is - you get what you asked for. If you didn’t ask, you might not get 