They don't. Shareaza never sends out Gnutella search results when not connected to Gnutella. However, there is another way that sources will spread around: The alternate source mesh. Unfortunately, sources from different networks may get mixed up in that source mesh, making G2-only sources appear in a Gnutella-only context. I'm not very sure about the current situation of this problem, and unlike what I was thinking first, this might have been taken care of already to some degree. However, fixing this problem in the various clients does not solve this problem yet. It's enough that some people use old clients (which are possibly buggy or misbehaving) of their favourite p2p client and this may cause G2 sources to appear in Gnutella context again. And of course, Gnutella clients have not much other choice than to believe the information they get.

I guess one of the best thing to do here is to tell everyone that use old clients to upgrade to the newest version. Or if some clients are still mixing up alternate sources, they must be fixed.

et voilà says Shareaza gives crappy speeds. But remember that while the upload bandwidth will get spread across all connected networks, the very same is also true for the download bandwidth, thus there's nothing unfair about it. Plus, by doing this, Shareaza acts as a nice bridge between different p2p networks; i.e. this brings contents of for example the eDonkey2000 network into the Gnutella network and the other way around.