metamerism surface effect
Two alternatives really - either you think you are using K only but the rip is actually using CMY which together give a brown-looking black - as Mike says switch off the icc to ensure K only is used as per the original file values.
But I don't think this is the case - as you say they are off and color dropper reports this.
So we are left with one answer - one which fits in with your description of it looking black in one lighting condition but different in another reflected type of viewing condition.
Might be easier to quote the great oracle Mr W. Ikipedia:
"The appearance of surface colors is defined by the product of the spectral reflectance curve of the material and the spectral emittance curve of the light source shining on it. As a result, the color of surfaces depends on the light source used to illuminate them"
I guess the combination of ink / media & lighting that creates this effect - and it is an "effect" rather than the measured value so there's little you can do.
I encountered this with the older Epson Surecolors 7600 / 9600 especially - a really strong bronze look to single K in prints but only in reflected light.
It's a part of the wonders of metamerism - I don't see it as a problem that needs fixing, rather a by-product of the process that makes all this possible in the first place.