a problem with tcp checksum

Hi all,

I am going frustrated since a wired problem with tcp checksum seem to always
happen. ;-( I really wish to see somebody throw some light on it. The
situation is as follows:

I am trying to inject TCP packets using libnet_build_tcp_options(),
libnet_build_tcp() and libnet_build_ipv4() (checksum automatically built).
When TCP payload size is odd in byte, the tcp checksum is always incorrect
(using ethereal to capture injected packets and check them); while if TCP
payload size is even in byte, everything seems working very well.

What I wish to know is do I need to manually change some parameters of
libnet_build_tcp_options(), libnet_build_tcp() or libnet_build_ipv4() when
the tcp payload size is odd in byte, in order to let libnet compute tcp
checksum correctly? If not, what shall I do to fix the problem? I am looking
forward to your help. Thank you very much in advance!

Regards,
Jee