Tryied your version of /etc/xinetd.d/poppassd restarted XInetD tried again the same test and got the same result...
Do not know how to check if this version use de /etc/pam.d/passwd file. at leasst I can tell you it exist and the content is #%PAM-1.0 auth required /lib/security/pam_stack.so service=system-auth account required /lib/security/pam_stack.so service=system-auth password required /lib/security/pam_stack.so service=system-auth
Another idea?