procbounce unsubs the sender

Occasionally procbounce detects an excessive number of bounces and proceeds to unsubscribe the sender, not the bouncing address. Have looked at procbounce and rc.request, but I can't find how this can happen. I am using the default bounce parameters, using 3.13.1 in a Solaris environment with the public (not Sun) sendmail. Any ideas? Del D. L. Kimbler, Ph.D., P.E. Professor, Industrial Engineering Clemson University Voice: (864)656-5645 Fax: (864)656-0795