I have a unusual issue in our streams environment(10.2.0.4) where the prebuilt conflict handler is being ignored for an update to a table on which the handler is set on.
We created a maximum type handler which uses a timestamp(which we update/set with a trigger) for the resolution column, however, when an update was executed on the source site the transaction failed on the destination site with an ORA-01403. I've checked all the usual suspects such as dba_apply_conflict_columns to make sure we have all the table columns defined in the handler. I've also looked at supplemental logging for the table, which we set up to unconditionally log all columns.
An ORA-01403 error is indicative of a Delete Conflict, not an Update Conflict. See Chapter 9 of the Oracle Streams Replication Administrator's Guide for a description of the different conflict types. The Prebuilt Conflict Handlers only deal with Update Conflicts. You will have to write a custom handler to deal with other conflict types.