Functional-based index

Hey all,

I have a question regarding functional-based indexes in 10gR2, more specifcially 10.2.0.3.

We noticed last week some of our functional-based indexes are not updating themselves. When we use a query using a functional-based index we get no rows returned.

Now I rebuilt the index in question and re-ran the query and suddenly records are returned.

I was not aware that functional-based indexes need to be rebuilt manually, I thought this was part of the database internal engine as this is the first time I notice this.

Does anyone have any feedback on this?

Thanks