Wim,
normally the CSS uses 1.1 but it will first start by sending 1.0 and then switch to 1.1
You can force 1.0 with the command 'keepalive type http non-persistent'
There are also a bug that was fixed for a problem of version.
CSCed85319 - CSS incorrectly bumping 1.1 keepalive to 1.0
You should verify that you have the fix.
Regards,
Gilles.