That's annoying - no easy way to remove the search-autocomplete entries!
ALL the entries are stored one by one in the registry. You may delete them (search.01, 02, etc.) and set the whole folder to "no access" for all useres, admins, etc. but I don't know the effect of this workaround on Shareaza - so do it at your own risk or just install the previous version...
If anyone knows or found an official switch in the advanced settings please tell here. What a smart idea to put a hard to remove autocomplete function in a filesharing software...