Forwarding issue (no replies)

Why would the following apache directives cause problems for haproxy.

RewriteRule ^/Microsoft-Server-ActiveSync /rpc.php
[PT,L,QSA]
RewriteRule .* -
[E=HTTP_MS_ASPROTOCOLVERSION:%{HTTP:Ms-Asprotocolversion}]
RewriteRule .* -
[E=HTTP_X_MS_POLICYKEY:%{HTTP:X-Ms-Policykey}]
RewriteRule .* -
[E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

Thanks in advance