xtrabackup_55 segfaults when defaults file's basename differs from my.cnf

xtrabackup_55 binary reads configuration file correctly only when its basename is my.cnf

[root@test-cent5-64-t504 ~]# xtrabackup_55 --defaults-file=/tmp/my.cnf --backup --target-dir=/root/backup/full2
xtrabackup_55 Ver 1.6 Rev 245 for 5.5.9 Linux (x86_64)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /var/lib/mysql
xtrabackup: Target instance is assumed as followings.
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:10M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 5242880
110514 3:12:16 InnoDB: Using Linux native AIO
>> log scanned up to (1597945)
[01] Copying ./ibdata1
     to /root/backup/full2/ibdata1
[01] ...done
xtrabackup: The latest check point (for incremental): '1597945'
>> log scanned up to (1597945)
xtrabackup: Stopping log copying thread.
xtrabackup: Transaction log of lsn (1597945) to (1597945) was copied.

If basename differs from my.cnf xtrabackup_55 segfaults:

[root@test-cent5-64-t504 ~]# xtrabackup_55 --defaults-file=/tmp/trololo --backup --target-dir=/root/backup/full2
Segmentation fault

(gdb) run
Starting program: /usr/bin/xtrabackup_55 --defaults-file=/tmp/trololo --backup --target-dir=/root/backup/full2
[Thread debugging using libthread_db enabled]
[New Thread 0x40a00940 (LWP 1312)]
[Thread 0x40a00940 (LWP 1312) exited]
[New Thread 0x40a00940 (LWP 1313)]
[Thread 0x40a00940 (LWP 1313) exited]

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff74d3b80 in strlen () from /lib64/libc.so.6
(gdb) bt
#0 0x00007ffff74d3b80 in strlen () from /lib64/libc.so.6
#1 0x0000000000530447 in fn_format (to=0xa02c80 "", name=0x7fffffffec8c "trololo", dir=<value optimized out>, extension=0x0, flag=196) at /usr/src/debug/xtrabackup-1.6/Percona-Server-5.5/mysys/mf_format.c:77
#2 0x000000000052f658 in fn_expand (conf_file=0x553681 "my", argc=<value optimized out>, argv=<value optimized out>, args_used=<value optimized out>, func=0x52e5c0 <handle_default_option>, func_ctx=0x7fffffffe640, default_directories=0xa06860)
    at /usr/src/debug/xtrabackup-1.6/Percona-Server-5.5/mysys/default.c:168
#3 my_search_option_files (conf_file=0x553681 "my", argc=<value optimized out>, argv=<value optimized out>, args_used=<value optimized out>, func=0x52e5c0 <handle_default_option>, func_ctx=0x7fffffffe640, default_directories=0xa06860)
    at /usr/src/debug/xtrabackup-1.6/Percona-Server-5.5/mysys/default.c:235
#4 0x000000000052fe3f in my_load_defaults (conf_file=0x553681 "my", groups=0x990f80, argc=0x7fffffffe71c, argv=0x7fffffffe710, default_directories=0xa02c58) at /usr/src/debug/xtrabackup-1.6/Percona-Server-5.5/mysys/default.c:550
#5 0x00000000004141f5 in main (argc=4, argv=0x7fffffffea48) at xtrabackup.c:5783
(gdb)