You have to look at its sources or ask the developers to get a definitive answer. Such queries might be caused by ed2k or magnet-links with such a hash. There's of course an urn:sha1 equivalent for each of them but you cannot calculate it before you have the file.

In theory you can use any urn-scheme you like and it will work as long as there are enough peers that support it. Using ed2k hashes is certainly questionable since ed2k has its own network which would be a much better choice for this. Maybe they added it because too many Shareaza users got kicked from the ed2k network.

Shareaza is widely known to do a lot but little correctly and it wouldn't be the first time that it bugged Gnutella like parasite. Exploiting the name "Gnutella" for publicity, abusing Gnutella to bootstrap the infamous G2, free-riding GWebCaches, downloading from Gnutella peers but blocking uploads to them are the well-known examples.