Phaser 850 using colour on black and white print runs

Hi all,

I have recently purchased a Phaser 850. We print booklets. I print the
covers off which use colour and have no problems at all. I am pleased
with the ink usage here.

However when I come to print the 8 inside pages of the booklet (duplex,
then folded into A5), I am using colour ink when I don't want to be.
The inside pages have been generated from publisher and printed to PDF
in black and white format. They are mainly text buy contain some
grayscale images. I then print these 8 pages (duplex) using the
following settings:

Print Quality: Fast Color
Color correction: Black and White (I've also tried "None").

These are set on the driver and on the printer itself. Even with these
on I am still getting 1% coverage from each colour ink, which goes
through colour quite quickly when printing 8000 pages! I don't want to
be using any colour ink at all for the inside pages, but just can't find
a way to stop the printer doing so.

Another interesting stats from the "Usage Profile" is line 131 which
logs all my supposedly "Black & White" printoffs as "Color".

Can anyone help me to use black only for the inside pages?

Thanks
JH