I don't know why the driver would switch to photo black ink if you have matte paper selected in the unclog job.  Are you sure matte paper is selected in the actual unclog job because each unclog job has its own printer settings?  You could be checking the current driver settings (which say matte paper) but the unclog job has glossy paper selected.  So even though the driver shows matte at the current moment, printer settings are part of the unclog job and if those have glossy paper selected, it will switch to glossy paper (as specified) before printing the unclog job.

Regards,
Mike