Callback on api.flukso.net

I'm developing a windows phone 7 api for flukso. As all http communication needs to be implemented async, i would need the callback to make a difference between the call's and responses.
This works perfectly on the local / reamtime requests, but not on the request to api.flukso.net.
Is this normal behavior or am I missing something out? The manual seems to make notice of the callback parameter for history requests to the api.