negative values in strace output.

[pravin]

hi
      I used strace to count system call using following command
strace -cfF tbench_srv

hardware : 8 way IBM x460 machine
Kernel : 2.6.13 and 2.6.14 linux
strace version : 4.5.9 and 4.5.11

But I have seen strange values like negative percentage and
negative time in seconds as given below.
Can anybody explain me this output or this is a bug in strace?

Regards,
Pravin.

Please cc me reply, since I am not on this mailing list.

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
-0.47  144.1207465          41   3530205           sendto
-0.00    0.901656      112707         8           mmap
-0.00    0.740029      740029         1           socket
-0.00    0.739791      739791         1           listen
-0.00    0.737944      737944         1           bind
-0.00    0.737793      737793         1         1 access
-0.00    0.737561      737561         1           uname
-0.00    0.737532      737532         1           arch_prctl
-0.00    0.737464      737464         1           lseek
-0.00    0.737460      737460         1           brk
-0.00    0.737449      737449         1           clone
-0.00    0.481101      240551         2           write
-0.00    0.477133      238567         2           munmap
-0.00    0.476060      238030         2           open
-0.00    0.475492      237746         2           mprotect
-0.00    0.475417      237709         2         1 wait4
-0.00    0.475204      237602         2           rt_sigaction
-0.00    0.475150      237575         2           read
-0.00    0.212929       70976         3           setsockopt
-0.00    0.212565       70855         3           fstat
-0.00    0.212493       70831         3           close
0.00   -1.553271     -223364         2         1 accept
100.51 -31102.605132       -4404   7060411           recvfrom
------ ----------- ----------- --------- --------- ----------------
100.00 -30946.884091              10590658         3 total