So i have noticed this issue alot, when stealthing sometimes you are not displayed graphically as invisible, but you have the invisible buff on.
same thing with moa, when i get moa by mesmer, its not a stealthed moa
in fast pace combat this makes it hard to tell if im stealthed or not, i sometimes use another cloak and dagger, thinking that im not stealthed, only for it to give me a revealed debuff.