Usually other monsters after being cursed show hurt numbers when they attack.
Lumbers, though, don't. I've tried this on T2 normal and ice lumbers with curse vials (T1 and T2 vials). They don't show any signs of getting hurt, and they take equal amounts of beating to die (even after the curse has worn off).

Does anyone else get this?

Edit: Just had a look at the monster bug anthology thread and turns out I should have read that first. -_- Take this thread as multiple occurences then.