when using remote.type = POST the params are send as the string "{object:object}".
I can make it work by changing
xhr.send(params);
to
xhr.send(paramsString);
in ajax.js#35
AND setting
headers: { 'Content-Type': 'application/x-www-form-urlencoded' }
As this requires configuration on the "user" side I do not consider this worth a patch, but would like to file the issue anyhow. Will have to investigate this further - or maybe someone else comes up with a better solution?