This has been bugging me for a long time and I finally complained about it and Tom Lane kindly gave a reason for the problem and that its by design and not a bug.
So I thought I would post the situation here without getting into too many embarassing specifics in case others have suffered from a similar fate and can learn from this.
You create a function lets call it myniftyfunc() in the public schema.
Then you create another function that depends on myniftyfunc(), lets call it mysuperniftyfunc() also in public schema.
Then because your function is such a super nifty function, you decide to create a functional index with that super function on your table that sits in mysuperdata schema - mysuperdata.mysupertable
Your super nifty function is doing its thing; your table is happy; the planner is spitting out your queries lightning fast using the super nifty index on your super table;
The world is good.
One day you decide to restore your nifty database backup and to your chagrin, your nifty index is not there. The planner is no longer happily spitting out your queries lighting fast and everything has come to a painful crawl.
Your super nifty index is gone. What happened to super nifty functional index?
I have to admit that I'm the type of person that assumes the public schema is always there and always in search_path and that my assumption is a flawed one. After all the public schema is there by default on new databases for convenience,
but one can change it not to be in the search_path and in fact pg_dump does just that. So if everything you have is kept in public schema -- you don't run into this particular misfortune. If however you have your functions in
public and your tables in different schemas, during restore -- the search path is changed to the schema being restored and your super functional indexes based on super functions that depend on other super functions fail because public is no longer in the search_path.