ah... alright! thats good news
i was already flippin' shit.. kinda
built a nice fort, realise "something" is missing...
was just new to me you can make stuff like this appear later when you found magma, i thought everything is in at start.
when i tried out the poisons i was kinda dissapointed at first, cause i thought they would be permanent... but they wasnt.
but the more i thought about it, that wasnt logical.
found nothing on the forums, so i tried stuff here and there.
without gloves on, the spatter was on their body, mostly on their hands after they hit enemies.
sometimes after 10-20 hits, sometimes after one, i think it depends on their bleeding.
with gloves, actually full leather armor, i never encountered the problem again.
only one time, when i got the equipment of my squad set on leather armor, not specific items.
i guess he was switching stuff when i sent him to kill some enemies, at least he lost the coatings on his spear.
the other soldier in the squad was fine, still 5 poisons on his weapon.
maybe its some kind of weird bug, but maybe you can replicate it.
funfact; the idea with gloves came from forgotten beast spatter and blood on weapons, poison coating the old way
anyways, i hope i could help you there.
feel free to ask anything specific there, if you need more information.
oh and no, it wasnt adv. mode, it was fortress mode. (not even sure how you get poison spatter there?)
edit: just to mention it, the weapon coatings are permanent, the spatter i got on the hands/body later weren't
they vanished with "clean all"