I have figured out why I was getting a number of unpredictable errors from backend classes employed as part of a plperlu function for PostgreSQL - The DBD::PgSPI database driver only supports a single connection! Trying to create a secondary connection to the database seemed to be causing very nasty things to happen.
What a headache it caused trying to figure out this one! Hopefully, this will be of use to others working with PostgreSQL.
