Ah, OK. Interesting.
When I post from my Google Buzz widget on my Android phone, nothing shows up on Twitter. But, if someone likes the Buzz post or comments on it, it does show up on Twitter. The problem though is when it does show up on Twitter, instead of having the text of the Buzz post followed by a link back to the original post on Buzz, it has the text of the Buzz post, followed by "Error: Please specify a URL to shorten."
In the particular instance I tried, the Buzz post had an image attached to it. Not sure if that makes a difference though.
(If it was just a text only Buzz from my phone, I could probably just use the actual Buzz mobile website and not the Buzz gadget. But, if I need to upload an image for my Buzz, you have to do that from the widget. At least I think you do, as I can't find a way to do that from the Buzz mobile website.)