When creating a SQL Agent step using the SSIS subsystem, adding a configuration entry with an UNC path is successful. Since adding an invalid path is impossible and raises an error, the user is lead to believe that path validation is occuring at configuration time and so a correct (and accepted) file UNC is a valid configuration.
At run time, however, behavior is far from expected. You must manually change the /REPORTING E parm to a V(erbose) to see the confusing runtime issues.
First, the job step runs and completes if the configuration settings in the original package are usable, but data may be coming from unexpected (e.g., develpment environment) sources without warning. Closer inspection of the resulting logs reveals the following:
1) DTExec ignores the UNC path entry, but it's presence in the configuration causes the attempt to use either the default server config path OR the config path used in the develpment environment if configured.
2) Even though the configured UNC file is not used AND the attempted config file is not present, the package raises no warnings or errors and continues to run using it's original configuration when deployed from BIDS.