mold... i think... best solution is to cut out the part that does not get rid of them after 1st or 2nd try with bleach or h2o2 solution. i found that keeping the baggie just moist and airing out, that means wrapping the paper towel everyday, helps a great deal. but if it's "set" into the cutting, it won't go away. physan20 is another solution. i never had to use the bottle i have.
one batch of cuttings i got this winter had serious mold issue. the cuttings were very fresh, but they were wrapped in very wet papers. i think during the transit, the weather was cold enough, they were frozen, and thawed. seems like mold and rot set in during that time and once i started rooting them, they stared massive mold and i just could not control it. sooner after the mold, rot set in, and the barks stared to peel off. i trashed the whole batch.
Panacea cuttings i got from jon during the winter were great. after processing, i had 10 cuttings. i kept three and sent rest to two members. out of 3, one was stuck into 1 gal pot, two were callused, and put into cups. one of the cutting in the cups made it and moved into a 1 gal. other two didn't make it.