White Outs Bleeding Through

I've been using a color for a long time as a white out in many of my
drawings. For some reason this week they quit working correctly on me
and I can't figure out why.

Basically what I've set up is a color with 100% screening, it's work
great for years for me. But this week it all went to crap. *SOME*
objects below the white out appeared to be bleeding through. Even
objects in paperspace that had a white out were bleading through. I
tried all the usual tricks for it. Coping the white outs raising them
on the Z axis and of course draw order but nothing worked. They were
clearly bleading through but not consistantly (which is what was
making me nutts.)

I thought it may have been the plotter driver issue so I created PDF's
of some of the drawings which appeared correct when I viewed them but
the plots of the PDF's came out the same way (with bleading of certain
objects.)

Can anyone help me save my sanity?!

Thanks in Advance
Russ