For me, it is like a bug as, in my opinion, that code should be independent of the unity catalog as it sparks code, and you don't register anything in the unity catalog. So please pass it to your databricks representative or as a support ticket.
There are SQL functions (udfs) in Unity, and soon there will be Python one, but it is about ones that are registered in meatstore/catalog.
Maybe the problem here is that you use a shared version, so it wants to register it so it will be available for other users?