'not a bug in need of Serious surgery to fix, but...
Sometimes when a lichen wanders into a niche when not attacking anyone, it starts oozing against the wall in a strange, inappropriate-ish-like manner... We can even stand next to it, charge, and then hack at it -- but it won't turn around 'till it's been knocked outta place. The lichen honestly won't turn around on its own. Of course, this doesn't happen with the larger lichen colonies.
Also, twice, when my whole party died, a lichen stuck oozing in a niche will squirm faster like it's trying to run through the wall. It's really, really weird looking.
Was there another lichen around? it could be attempting to fuse, but failing at pathfinding its partner.