Digital BW, The Print

I have two questions:
1.  I made some proof prints today on Epson heavyweight matte, using my 
C84 with EZN inks, and I'm seeing a green color casting in daylight. This 
printer has never had color inks in it. Am I crazy, or is this possible?

2.  I read in Clayton Jones' online articles that after turning an image to 
monochrome in channel mixer, I should convert it to grayscale (image/mode) 
before doing my work and then back to RGB again before printing. It also 
suggest converting to 16-bit to do work on the image, and then back to 8-bit 
before printing. I've always worked in 8-bit RGB and never converted to 
grayscale or 16-bit before. What is the purpose of this, and could it have 
caused #1 above?

Cheers,
George Le Masurier