You can/should confirm false positives yourself. Upload the file in question to Jotti at http://virusscan.jotti.org/
on the Web or to VirusTotal at http://www.virustotal.com/
on the Web. Either service will provide a free scan of your file with multiple antivirus programs. If more than a couple of other AVs besides Clam find a file is infected, it probably is.
You can submit both infected files and false positive files to Clam at http://cgi.clamav.net/sendvirus.cgi
on the Web. For false positives, be sure to insert the name of the false positive on the form and check the false positive box.