Empty IP when forwardfor enabled

[Rodrigo]

Hi,

I've setup two frontends balanced with Haproxy 1.3.15.7 (excellent software)
in another server:

       Load balancer
              / \
            /    \
           /      \
Frontend 1    Frontend 2

I have enabled "option forwardfor". I have set LogFormat in Apache
configuration file as follows:

LogFormat "%{X-Forwarded-For}i  %l %u %t \"%r\" %>s %b \"%{Referer}i\"
\"%{User-Agent}i\"" combined

but many times the IP field appears empty. I've read on this mailling list
that it has something to do with KeepAliveTimeout on Apache. I rised up it
from 6 to 15, but no luck.

How could I fix this?

Thank you