I know what you mean - it's a pretty big call though, because changing that affects any other item that works similarly.
I like that items such as the Potion of Life get consumed right away: it adds a bit of risk to the whole thing, because if you get hit, stunned or slept before the cast is over, the item is gone - wasted. That means you have to pick the right time to use it - instead of just trying and retrying and retrying.
It makes sense "lore" wise too - if you use the Potion of Life, you start feeding it to whoever you used it on - or if you use the Thunderstone, you're doing something with it (breaking it apart?) that unleashes its magic (which is symbolized by the cast bar). If you stop doing it - would the rest of the item still be good?
It's a tough call, because on one hand, I understand it's frustrating consuming an item due to a mistake - on the other hand it does make it more risky, and thus requires players to spend a greater amount of thought on just when they'll use it - instead of blindly going by trial and error.
