I used to use Hemo-De (citrus-based) to coverslip with.  Once, in a hurry to dry the slides to send them out, I put them in a 70 degree oven on slide trays (which is the way the routine Histo Lab dries their slides before filing them).  When I took them out of the oven, the Hematoxylin and DAB were both gone.  I don't know the reason why this happened, but I wasn't anxious to see if it would happen again.

Julie