Digital BW, The Print

Hello there, I am a new memeber of this group. I wonder if any of you 
out there has experience with BO printing on Epson 2200 as described 
in the essays written by Clayton Jones. 
I tried his recommended procedure with Epson Matte Ink and epson 
Enhanced Matte paper and got an print that has a brown cast - almost 
like a duotone - definitely not metamerism. The same image printed 
with the same ink/paper set with Imageprint RIP produced a perfect 
grey-scale print. Am I observing a characteristic of Epson matte ink 
with BO setting?
thank you for any feedback I recieve.
cheers
vartkes