It looks like there might be a slight issue with the ProxyPass iRule's use of 'HTTP::header replace'. Can you find this line:
HTTP::header replace Host: $host_serverside
and replace it with this line?
HTTP::header replace Host $host_serverside
and this line:
HTTP::header replace $header: $protocol$host_clientside$path_clientside[substr $server_path [string length $path_serverside]]
with this line:
HTTP::header replace $header $protocol$host_clientside$path_clientside[substr $server_path [string length $path_serverside]]
and then retest?
Thanks,
Aaron