Delirious map not increasing percentage on killing rares sometimes

When running a delirious areas (from a grand mirror), I noticed if I use a delirium tablet I no longer get percentage increases when I kill rare monsters, like when i have abyss tablets or no tablets. I did notice getting tons of simulacrum splinters with 3 deli tabs which was nice, perhaps intended.

However, what I doubt is intended is sometimes with no tablets I still don't get percentage increase on rare kills. My guess is, if the map randomly chooses delirium as a mechanic to spawn, but it's a delirious area, you just don't get percentage increases on rares, and just get some splinters. maybe still intended but not intuitive.