dovecot crashing

[cheese at nosuchhost.net]

i have a system with panics/crashes and seem to be able to trigger the 
problem.

dovecot version: 2.2.33.2 (from ius rpm-package-repository)
maillog:

Dec 14 10:55:00 vimap01 dovecot: imap(XXX): Panic: file index-mail-binary.c: line 358 (blocks_count_lines): assertion failed: (block_count == 0 || block_idx+1 == block_count)
Dec 14 10:55:00 vimap01 dovecot: imap(XXX): Error: Raw backtrace: /usr/lib64/dovecot/libdovecot.so.0(+0x9f3de) [0x7fa6768ef3de] -> /usr/lib64/dovecot/libdovecot.so.0(+0x9f4be) [0x7fa6768ef4be] -> /usr/lib64/dovecot/libdovecot.so.0(i_fatal+0) [0x7fa67688077c] -> /usr/lib64/dovecot/libdovecot-storage.so.0(+0xb50f7) [0x7fa676c370f7] -> /usr/lib64/dovecot/libdovecot-storage.so.0(index_mail_get_binary_stream+0x3c9) [0x7fa676c37569] -> /usr/lib64/dovecot/libdovecot-storage.so.0(mail_get_binary_size+0x5b) [0x7fa676bbfa2b] -> /usr/lib64/dovecot/libdovecot-storage.so.0(imap_msgpart_size+0x80) [0x7fa676c7a340] -> dovecot/imap(+0x207a9) [0x55b9589327a9] -> dovecot/imap(+0x1e63a) [0x55b95893063a] -> dovecot/imap(imap_fetch_more+0x35) [0x55b958931b45] -> dovecot/imap(cmd_fetch+0x34d) [0x55b95892336d] -> dovecot/imap(command_exec+0x5c) [0x55b95892ef0c] -> dovecot/imap(+0x1b48f) [0x55b95892d48f] -> dovecot/imap(+0x1b521) [0x55b95892d521] -> dovecot/imap(client_handle_input+0x195) [0x55b9589
 2d8e5] -> dovecot/imap(client_input+0x85) [0x55b95892de05] -> /usr/lib64/dovecot/libdovecot.so.0(io_loop_call_io+0x52) [0x7fa676904cd2] -> /usr/lib64/dovecot/libdovecot.so.0(io_loop_handler_run_internal+0x10f) [0x7fa6769063bf] -> /usr/lib64/dovecot/libdovecot.so.0(io_loop_handler_run+0x3c) [0x7fa676904d6c] -> /usr/lib64/dovecot/libdovecot.so.0(io_loop_run+0x38) [0x7fa676904f28] -> /usr/lib64/dovecot/libdovecot.so.0(master_service_run+0x13) [0x7fa67688afa3] -> dovecot/imap(main+0x333) [0x55b9589202e3] -> /lib64/libc.so.6(__libc_start_main+0xf5) [0x7fa6764aec05] -> dovecot/imap(+0xe476) [0x55b958920476]
Dec 14 10:55:00 vimap01 dovecot: imap(XXX): Fatal: master: service(imap): child 5766 killed with signal 6 (core dumped)

gdb backtrace is attached as file

more infos/core-dump-file available if needed.

yours
josef

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