Digital BW, The Print

Hi out there,
I just printed test patches with IJC/OPM and MIS UT7 inkset with an
EPSON 2100 on a sheet of Hahnem�hle Fine Art Pearl. After drying
several hours I could smear the black (only the black) ink with my
fingers! Dmax was 1.44!
What's the reason for that behaviour? 
I use eboni black, but I read this ink could also be used for glossy
papers.
Has anyone made the same experiences?

Thanks
Gerd