I finally managed to get the crash while gdb was tracing the dbus process. This time it was not a bogus SIGPIPE. Again, this happened while shutting down a host of processes running on dbus. 

I have saved the core file, so if you need anything else, let me know.

Backtrace:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 140407117903744 (LWP 11324)]
0x0000000000e1a012 in strcmp () from /lib64/libc.so.6
(gdb) bt full
#0  0x0000000000e1a012 in strcmp () from /lib64/libc.so.6
        mallstream = (FILE *) 0x0
        tr_old_memalign_hook = (void *(*)(size_t, size_t, const void *)) 0
        tr_old_malloc_hook = (void *(*)(size_t, const void *)) 0
        tr_old_realloc_hook = (void *(*)(void *, size_t, const void *)) 0
        lock = 0
        mallenv = "MALLOC_TRACE"
        malloc_trace_buffer = 0x0
        tr_old_free_hook = (void (*)(void *, const void *)) 0
        mallwatch = (void *) 0x0
#1  0x00007fb31467abee in find_generic_function (table=0x7fb3155893f0, key=0x7fb3155973b0, idx=10, 
    compare_func=0xe1a010 <strcmp>, create_if_not_found=1, bucket=0x0, preallocated=0x7fb315607828)
    at dbus-hash.c:918
        entry = (DBusHashEntry *) 0x7fb3156077f8
#2  0x00007fb31467aea6 in find_string_function (table=0x7fb3155893f0, key=0x7fb3155973b0, 
    create_if_not_found=1, bucket=0x0, preallocated=0x7fb315607828) at dbus-hash.c:952
No locals.
#3  0x00007fb31467a8b1 in _dbus_hash_table_insert_string_preallocated (table=0x7fb3155973b0, 
    preallocated=0x7fb315607828, key=0x7fb3155973b0 "developer", value=0x7fb3155ab350) at dbus-hash.c:1680
        entry = <value optimized out>
#4  0x00007fb31467aad9 in _dbus_hash_table_insert_string (table=0x7fb3155893f0, 
    key=0x7fb3155973b0 "developer", value=0x7fb3155ab350) at dbus-hash.c:1443
        preallocated = (DBusPreallocatedHash *) 0xffffff64
#5  0x00007fb31468171e in _dbus_user_database_lookup (db=0x7fb315589260, uid=500, username=0x7fb3155e9fb0, 
    error=0x0) at dbus-userdb.c:208
        info = (DBusUserInfo *) 0x7fb3155ab350
#6  0x00007fb3146817e3 in _dbus_user_database_get_username (db=0x7fb3155973b0, username=0xa, 
    info=0x7fff1c69b610, error=0xffffffff) at dbus-userdb.c:661
No locals.
#7  0x00007fb314681a2d in _dbus_credentials_add_from_user (credentials=0x7fb3155eb8d0, 
    username=0x7fb3155e9fb0) at dbus-userdb.c:507
        db = (DBusUserDatabase *) 0xffffff64
        info = (const DBusUserInfo *) 0x7fb3155e9f60
#8  0x00007fb3146875fe in handle_server_data_external_mech (auth=0x7fb3155e9f60, data=0x7fff1c69b650)
    at dbus-auth.c:1065
No locals.
#9  0x00007fb3146867cb in process_data (auth=0x7fb3155e9f60, args=0x7fff1c69b6a0, 
    data_func=0x7fb3146874f0 <handle_server_data_external_mech>) at dbus-auth.c:1606
        end = 6
        decoded = {dummy1 = 0x7fb315595160, dummy2 = 3, dummy3 = 16, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 0, dummy8 = 0}
#10 0x00007fb3146869eb in handle_server_state_waiting_for_auth (auth=0x7fb3155e9f60, 
    command=<value optimized out>, args=0x7fff1c69b720) at dbus-auth.c:1658
        i = 9
        mech = {dummy1 = 0x7fb3155e4750, dummy2 = 8, dummy3 = 16, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 0, dummy8 = 0}
        hex_response = {dummy1 = 0x7fb3155abc20, dummy2 = 6, dummy3 = 16, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 0, dummy8 = 0}
#11 0x00007fb314685f82 in _dbus_auth_do_work (auth=0x7fb3155e9f60) at dbus-auth.c:2100
No locals.
#12 0x00007fb31467896f in _dbus_transport_get_is_authenticated (transport=0x7fb3155ecb60)
    at dbus-transport.c:688
        allow = <value optimized out>
        auth_identity = <value optimized out>
#13 0x00007fb314679318 in do_authentication (transport=0x7fb3155ecb60, do_reading=1, do_writing=0, 
    auth_completed=0x7fff1c69b85c) at dbus-transport-socket.c:422
        oom = <value optimized out>
        orig_auth_state = <value optimized out>
#14 0x00007fb314679bbb in socket_handle_watch (transport=0x7fb3155973b0, watch=<value optimized out>, 
    flags=<value optimized out>) at dbus-transport-socket.c:837
        auth_finished = <value optimized out>
#15 0x00007fb31467888d in _dbus_transport_handle_watch (transport=0x7fb3155ecb60, watch=0x7fb3155ec130, 
    condition=1) at dbus-transport.c:851
        retval = 1
#16 0x00007fb31466ed88 in _dbus_connection_handle_watch (watch=0x7fb3155ec130, condition=1, 
    data=0x7fb3155ec920) at dbus-connection.c:1420
        connection = <value optimized out>
        retval = <value optimized out>
        status = <value optimized out>
#17 0x00007fb314679f71 in dbus_watch_handle (watch=0x7fb3155ec130, flags=1) at dbus-watch.c:663
        __FUNCTION__ = "dbus_watch_handle"
#18 0x00007fb314682382 in _dbus_loop_iterate (loop=0x7fb3155856b0, block=1) at dbus-mainloop.c:810
        wcb = (WatchCallback *) 0x7fb31559a8c0
        condition = 1
        retval = 0
        fds = (DBusPollFD *) 0x7fff1c69bb10
        stack_fds = {{fd = 3, events = 1, revents = 0}, {fd = 9, events = 1, revents = 0}, {fd = 11, 
    events = 1, revents = 0}, {fd = 13, events = 1, revents = 0}, {fd = 12, events = 1, revents = 0}, {
    fd = 14, events = 1, revents = 0}, {fd = 17, events = 1, revents = 0}, {fd = 19, events = 1, 
    revents = 0}, {fd = 16, events = 1, revents = 0}, {fd = 18, events = 1, revents = 0}, {fd = 22, 
    events = 1, revents = 0}, {fd = 21, events = 1, revents = 0}, {fd = 20, events = 1, revents = 0}, {
    fd = 26, events = 1, revents = 0}, {fd = 15, events = 1, revents = 1}, {fd = 25, events = 1, 
    revents = 0}, {fd = 29, events = 1, revents = 0}, {fd = 31, events = 1, revents = 25}, {fd = 31, 
    events = 1, revents = 0}, {fd = 32, events = 1, revents = 17}, {fd = 32, events = 1, revents = 0}, {
    fd = 32, events = 1, revents = 0}, {fd = 32, events = 1, revents = 0}, {fd = 32, events = 1, 
    revents = 0}, {fd = 33, events = 1, revents = 17}, {fd = 33, events = 1, revents = 0}, {fd = 40, 
    events = 1, revents = 0}, {fd = 40, events = 1, revents = 0}, {fd = 40, events = 1, revents = 0}, {
    fd = 40, events = 1, revents = 0}, {fd = 40, events = 1, revents = 0}, {fd = 40, events = 1, 
    revents = 0}, {fd = 40, events = 1, revents = 0}, {fd = 41, events = 1, revents = 17}, {fd = 0, 
    events = 0, revents = 0}, {fd = 0, events = 0, revents = 0}, {fd = 0, events = 0, revents = 0}, {
    fd = 14494885, events = 0, revents = 0}, {fd = 342275856, events = 32691, revents = 0}, {
    fd = 342377564, events = 32691, revents = 0}, {fd = 342275856, events = 32691, revents = 0}, {fd = 0, 
    events = 0, revents = 0} <repeats 16 times>, {fd = 0, events = 32691, revents = 0}, {fd = 344591216, 
    events = 32691, revents = 0}, {fd = 342342956, events = 32691, revents = 0}, {fd = 0, events = 0, 
    revents = 0}, {fd = 0, events = 0, revents = 0}, {fd = 0, events = 0, revents = 0}, {fd = 0, 
    events = 0, revents = 0}}
        n_fds = 15
        watches_for_fds = (WatchCallback **) 0x7fff1c69b910
        stack_watches_for_fds = {0x7fb31558bc50, 0x7fb315590070, 0x7fb315590cf0, 0x7fb315594860, 
  0x7fb315591670, 0x7fb3155951a0, 0x7fb31559d440, 0x7fb31559f7c0, 0x7fb31559eb20, 0x7fb3155a5ea0, 
  0x7fb3155aa950, 0x7fb3155a9c10, 0x7fb3155a86e0, 0x7fb315598ff0, 0x7fb31559a8c0, 0x7fb3155a74e0, 
  0x7fb3155ebaa0, 0x7fb3155eab30, 0x7fb3155eab30, 0x7fb3155bdeb0, 0x7fb3155bdeb0, 0x7fb3155bdeb0, 
  0x7fb3155bdeb0, 0x7fb3155bdeb0, 0x7fb315644120, 0x7fb315644120, 0x7fb3155f6910, 0x7fb3155f6910, 
  0x7fb3155f6910, 0x7fb3155f6910, 0x7fb3155f6910, 0x7fb3155f6910, 0x7fb3155f6910, 0x7fb31560ca80, 
  0xf375846, 0x7fff1c69bb78, 0x7fb314631bc0, 0x1193ef, 0x0, 0x7fb314631bc0, 0x5, 0x0, 0x7fff00000001, 
  0x118deb, 0x0, 0x7fb314631b30, 0x6, 0x9, 0x0, 0x1001191f1, 0x7fb314655358, 0x7fff1c69bbe0, 
  0x7fb314655000, 0x7fb314657885, 0x0, 0x7fb314631b78, 0x14631000, 0x7fb314657971, 0xdb1000, 
  0x7fb314656ad8, 0x500000000, 0x1000001f1, 0x7fb314655000, 0x7fb314655358}
        i = 14
        link = (DBusList *) 0x1
        n_ready = <value optimized out>
        initial_serial = <value optimized out>
        timeout = <value optimized out>
        oom_watch_pending = 0
        orig_depth = 1
#19 0x00007fb3146824cd in _dbus_loop_run (loop=0x7fb3155856b0) at dbus-mainloop.c:874
        our_exit_depth = 0
#20 0x00007fb31466bda1 in main (argc=7, argv=<value optimized out>) at main.c:464
        val = 4
        end = 1
        error = {name = 0x0, message = 0x0, dummy1 = 1, dummy2 = 0, dummy3 = 0, dummy4 = 0, dummy5 = 0, 
  padding1 = 0x100562f70}
        config_file = {dummy1 = 0x7fb3155853b0, dummy2 = 24, dummy3 = 32, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 1, dummy8 = 0}
        addr_fd = {dummy1 = 0x7fb3155854f0, dummy2 = 1, dummy3 = 16, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 1, dummy8 = 0}
        pid_fd = {dummy1 = 0x7fb315585510, dummy2 = 1, dummy3 = 16, dummy4 = 2147483639, dummy5 = 0, 
  dummy6 = 0, dummy7 = 1, dummy8 = 0}
        prev_arg = 0x7fff1c69dbe5 "--session"
        print_addr_pipe = {fd_or_handle = -1}
        print_pid_pipe = {fd_or_handle = -1}
        i = <value optimized out>
        print_address = 1
        print_pid = 1
        force_fork = 1

(gdb) info threads
  2 Thread 1096554832 (LWP 11326)  0x000000000077776c in recvfrom () from /lib64/libpthread.so.0
* 1 Thread 140407117903744 (LWP 11324)  0x0000000000e1a012 in strcmp () from /lib64/libc.so.6