I've been using dfcleanmap routinely for probably several game years now because of this issue. The culprit is the one-eyed monster extract (ha ha but seriously that's what its called) the goblin leader left after his death, and anything more than the slightest contact causes blistering and, eventually, paralysis culminating in death by suffocation. A year or two after the last reported case sleeping sicking I decided to make some clear glass blocks for my barracks' skylight. I cued up some potash and pearlash and forgot about it--until I saw the dreaded "Potash maker cancels job: Paralyzed" pop up. I zoom to him and see that he's standing in an entire pile of the deadly extract along with several pages worth of other contaminants. Not only that, but instead of having blistered feet as the dwarves who went down to this stuff usually did, he had blisters on his mouth and hand. He died pretty soon after that. I has able to repeat this a couple times, although quick use of the clean map tool prevented any further deaths or injuries. Somehow, the start (not the completion) of the make potash job is releasing a large amount of a variety of contaminants, despite the lack of any on the ash. The amount varies as I repeat it; while the first looked like least 3.5 pages of pools of different liquids (I can't be positive it wasn't two combined), the last two together have only two pages of smatterings and a few pools of pus, ichor, and various bloods that didn't even include the dreaded extract.
Has anyone else ever seen anything like this?