Setting mbox_min_index_size above zero and accessing a small mbox triggers the panic in index_storage_mailbox_init() at dovecot-1.0.rc25/src/lib-storage/index/index-storage.c:368

dovecot: Mar 03 01:28:03 Error: IMAP(user): in-memory index creation failed. dovecot: Mar 03 01:28:03 Error: IMAP(user): Raw backtrace: imap [0x80b52c4] -> imap [0x80b4d59] -> imap(index_storage_mailbox_init+0x35e) [0x808d1ce] -> imap [0x806faec] -> imap [0x806fc99] -> imap [0x806fe98] -> imap(_cmd_select_full+0x83) [0x8059f43] -> imap(cmd_select+0x19) [0x805a139] -> imap [0x805bb85] -> imap [0x805bb0f] -> imap(_client_input+0x7c) [0x805bccc] -> imap(io_loop_handler_run+0x108) [0x80bb648] -> imap(io_loop_run+0x20) [0x80babe0] -> imap(main+0x4ae) [0x8063efe] -> /lib/libc.so.6(__libc_start_main+0xe6) [0xb7e46856] -> imap [0x8056991] dovecot: Mar 03 01:28:03 Error: child 2321 (imap) killed with signal 6

The immediate cause seems to be that mail_index_open_files() in dovecot-1.0.rc25/src/lib-index/mail-index.c returns zero at line 1536.