database not enforcing unqiue constriant

My previous employer contacted me today. Apparently they are having
an increasing frequency of occurances where they disocover violations
of the primary key constraint not being caught by the database. This
system is an ISAM emulation system, and it relies heavily on the
database throwing unique constraint violations to approximately
provide a cobol rewrite statement.

These errors are never caught when they occur. One way they are
caught is during a dump/reload, the record fails to reinsert.

I brought this up around a year ago, and the issue was never
successfully resolved. These are windows systems running PostgreSQL
8.0.x.

any thoughts?

merlin