This is Geisha Girl, mentioned above. This is definitely a problem. It also affected another MM of mine on a similar mission in some caves rather than sewers. Until it is fixed, I guess I'll have to avoid Lorenzo as a contact for my MM's. It's definitely no fun suddenly facing a half-dozen each of fungoids, bladegrasses, and bedrocks along with a couple of LT variants.
Edit: The arc name is "An Unnatural Order" Part 7.