Digital BW, The Print

I have had a variety of bad results trying to print B&W images on my 
1270. But during the latest run at adjusting the color balance, 
transfer function, etc I was surprised to find that on my printer at 
least, sending a greyscale image from photoshop to the Epson using 
the 'sepia' default produced a nice, cool image -- not at all what I 
was expecting. 'Monochrome', by the way, produced a warmish image 
with a greyscale input. Certainly the best B&W I have ever managed to 
excrete. If I use an RGB tagged greyscale image one gets the expected 
reddish chocoloate.

Can anyone help me to understand what is going on here? Is this 
a 'feature' of the NT4 Epson driver with Photoshop6? i.e. a bug. 
Might this property just go away with another version of the driver?

I am using the standard Epson dye inks on Heavyweight Matt.

thanks