iControl REST 404 despite success when adding pool member

I execute the following cURL POST to add a pool member and receive a 404:

curl -k -X PUT -H "Authorization: Basic xxxxxx" -H "Content-Type: application/json" -H "Cache-Control: no-cache" -d '{"name": "10.10.10.10:11"}' "https://localhost/mgmt/tm/ltm/pool/~Common~testpool/members" | python -m json.tool`

Result:

{
    "code": 404,
    "errorStack": [],
    "message": "Object not found - 10.10.10.10:11"
}

The weird part is that despite the 404, the cURL is successful. The pool member is added exactly as intended. My LTMs are on 11.5.3 HF2, is this a known issue? Is there any other way to accomplish this that returns a proper 200 and doesn't impact pool members that already exist?