There's an RFE for this, BZ222409. You could open a case with F5 Support and ask them to attach it to the RFE.
For now, you can add logic to your iRule to handle relative and absolute URIs:
http://devcentral.f5.com/Community/GroupDetails/tabid/1082223/asg/50/aft/1178966/showtab/groupforums/Default.aspx1249734
when HTTP_REQUEST {
Check for an absolute URI
if {not ([HTTP::uri] starts_with "/")}{
if {[scan $abs_uri {%[^/]//%[^/]%s} proto host uri] == 3}{
Log the URI to a local URI
log local0. "\$proto: $proto, \$host: $host, \$uri: $uri"
}
}
}
Aaron