They've got common prefixes, which is probably why this happened (the auto artist search is prefix based). I don't know if this can or should be fixed. It seems too aggressive in this case, but I can see how it would be useful for artists with a dedicated URL with multiple image directories. People should be careful when using the automatic artist search though if it's going to make these sorts of assumptions.
On a related matter, I couldn't find a proper name on the website anywhere and the artist uses "tamaya" in his URL and e-mail address but signs the pictures "bonnou oukoku", which would be preferred in this case?
