I'm not really sure what is happening here... we pass the page you are on as a query string param to Live ID, and it sends you back to that page... so to end up a different page would *likely* mean we passed the wrong URL, but that is rather simple code (it just grabs the current URL) and it certainly doesn't seem to be happening all the time. I'll try to repro it myself a few times, but if you find out any more information (like it always happens with the same post, or something like that) just let us know.
And if anyone else is seeing this, please post here as well.