I'm wearing the muffle enchanted dark brotherhood boots and using the invisibility spell and yet draugr and npcs etc. Still always discover me if i get too close to them.
I would have thought that muffle together with invisibility would make me completely undetectable until I attack or activate something.

I heard muffle spell only counts for 50% of noise reduction and the other half has to come from other items/perks.

inviaibility works like chameleon now. it just makes you harder to detect. one question:were you sneaking?

Dunno if it's the same, but...I have to un-equip and re-equip the backstab gloves to get them working properly. Maybe the same issue plagues the boots.

Or maybe it's just bugged like a lot of things.

If it only reduces the noise by 50%, the items/spell should say but they don't..

Yes.