It also may just be so intermittent that people never notice, or can't tell mis-matched notes from the general idiocy exhibited by many notes. At any rate, it's certainly still possible, so I'd strongly recommend against using the service for any important collaborations. In light of what's already been said, the answer to that is trivial. While browsers may render content in different ways, you could always be assured that only your content was driving the browser. With Third Voice, that is not the case.
Foreign content is inserted into the page by the processes outlined above.
This does not constitute a proof that Third Voice is bad. I know that. Most people I've seen confronted with the above react as if I think it is a proof that Third Voice is bad. Of course it's not a proof. It's a direct answer to the assertion that using Third Voice is just like using an alternative browser, which, as I believe I've shown, is false.