CMIS update does not work via share proxy

Doing a CMIS update via the share proxy does not work.
I suspect that the POST parameters are not being correctly passed through.

e.g.
In the following example the first curl command does not work whereas the second one does (or you can just modify the URL and see it work/not work)
(Auth is for admin/admin - tested against an unmodified SDK build)

DOCID=fe5828a8-9503-47ec-8f8f-2b33c1c0c995
curl 'http://localhost:8080/share/proxy/alfresco-api/default/public/cmis/versions/1.1/browser/root' -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8' -H 'Authorization: Basic YWRtaW46YWRtaW4=' --data "cmisaction=update&objectId=${DOCID}%3B1.0&propertyId%5B0%5D=cmis%3Adescription&propertyValue%5B0%5D=&propertyId%5B1%5D=cmis%3Aname&propertyValue%5B1%5D=File1&propertyId%5B2%5D=cm%3Atitle&propertyValue%5B2%5D=file1+title&propertyId%5B3%5D=cm%3Adescription&propertyValue%5B3%5D=description1"

curl 'http://localhost:8080/alfresco/api/default/public/cmis/versions/1.1/browser/root' -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8' -H 'Authorization: Basic YWRtaW46YWRtaW4=' --data "cmisaction=update&objectId=${DOCID}%3B1.0&propertyId%5B0%5D=cmis%3Adescription&propertyValue%5B0%5D=&propertyId%5B1%5D=cmis%3Aname&propertyValue%5B1%5D=File1&propertyId%5B2%5D=cm%3Atitle&propertyValue%5B2%5D=file1+title&propertyId%5B3%5D=cm%3Adescription&propertyValue%5B3%5D=description2"