So when you steal an item, it appears in your hands. So if someone looks at you, you walk out of the room or put it away, they are going to see it. Most pickpocket IRL happens in the open, not the shadows, dippers don't hide, they distract. As it works right now, you need to do everything in the shadows.
Because if you don't hide from the start, as soon as the person you stole from realizes you are missing (you sneaked out), you are going to be the first person they suspect when they check their inventory (which players do a lot).
There are ways to go around it, for example awaiting in the shadows and having the person leave the room, but it makes life really difficult for the thief since sneaking around everywhere is rather taxing on the body and also there are places where you can't hide at all, not to mention that if you are in a public venue like bar, other people may notice you sneaking around, which will get you in trouble immediately, unless you are the best ninja in town which most likely you are not.
I am not 100% on this, but I think also putting away things in your inventory breaks stealth, I could be wrong tho.
So my 'idea' is simply, when you steal something it goes into your inventory and not in your hands, straight away and or for putting away items not to break stealth (if it already doesn't work that way). That's it.