The special filter field "Schema=" can be used to override the default database schema (that will be used in the query) with the one specified in the Filter parameter following "Schema="
This special filter is designed to be used with NL() functions that return specific values.
In NL() functions where the "Field" parameter is either left blank or contains a specified field cache, "Schema=" will return the correct data, but any NF() functions that reference that field cache cannot recognize the "Schema=" restriction.
To accomplish the desired results, it is a simple matter to make a slight design change in a report.
Instead of attempting to use an NF() function to reference an NL() function which utilizes the "Schema=" filter field...
change your NL() function to return the specific field for which you were using the NF function:
Or have the NL() function return a reference-able value and then use an NL("First") function to return the desired field (referencing the value returned by the first NL() function as a filter):