Further to my previous email I managed to find the core file.

Version: 1.0.beta9 OS: Gentoo x86

Core was generated by `dovecot-auth'. Program terminated with signal 11, Segmentation fault.

(gdb) bt full #0 0xb7d575ba in strcasecmp () from /lib/tls/libc.so.6 No symbol table info available. #1 0x0805b091 in passdb_get_credentials () No symbol table info available. #2 0x00000000 in ?? () No symbol table info available.