It depends on their code, I guess.
I remember EQ having to globally effect a whole category, to change one thing within it, because their code wasn't as well written as it could be... and it got modified/convoluted over time.

I'd imagine Blizzard's code is better written... with a larger team, and being a later released game, they have the ability to look at predecessors and avoid their mistakes.
So there is also a good chance, this is a bug.
Or maybe it was a fix for the said treasure chest, but the global action is the bug.