The current documentation for the id parameter states: http://build.fhir.org/subscription-operation-status.html

"At the Resource level, one or more parameters containing one or more comma-delimited FHIR ids of Subscriptions to get status information for. In the absense of any specified ids, the server returns the status for all Subscriptions available to the caller. At the Instance level, this parameter is ignored."

This is confusing. We need to differentiate between how the id parameter behaves for GET vs POST. EG: in POST, you are expected to pass in a new parameter for each id. In GET, you are separating the id parameter by commas. 

In addition, the "In the absense of any specified ids, the server returns the status for all Subscriptions available to the caller" - this should only apply to Subscription/$status and not Subscription/[id]/$status