Please take a screenshot of the Printer Settings portion of your printer dialog box and post it here.
Here is the print dialog box from acrobat 9.0.0 with plain paper selected. the matte black ink was already in use and i didnt want to charge the PK just for a few sheets of A4. I was quite happy when i saw i had the option to choose MK as i didnt recall seeing this before. Needless to say all in vain. the 3800 still charged the PK and printed on the plain paper.