Accept Header is not honored / Errors returned in XML instead of JSON

$ http http://localhost:8983/solr/offers_gb/select q==*:* wt=json rows=1 Accept:"application/json" -v
POST /solr/offers_gb/select?q=%2A%3A%2A HTTP/1.1
Accept: application/json
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 27
Content-Type: application/json
Host: localhost:8983
User-Agent: HTTPie/0.9.4

{
    "rows": "1",
    "wt": "json"
}

HTTP/1.1 400 Bad Request
Content-Length: 525
Content-Type: application/xml; charset=UTF-8

<?xml version="1.0" encoding="UTF-8"?>
<response>
<lst name="responseHeader"><int name="status">400</int><int name="QTime">0</int><lst name="params"><str name="q">*:*</str><str name="json">{"wt": "json", "rows": "1"}</str></lst></lst><lst name="error"><lst name="metadata"><str name="error-class">org.apache.solr.common.SolrException</str><str name="root-error-class">org.apache.solr.common.SolrException</str></lst><str name="msg">Unknown top-level key in JSON request : wt</str><int name="code">400</int></lst>
</response>

$ http http://localhost:8983/solr/offers_gb/select q==bla:* wt==json rows==1 Accept:"application/json" -v
GET /solr/offers_gb/select?q=bla%3A%2A&wt=json&rows=1 HTTP/1.1
Accept: application/json
Accept-Encoding: gzip, deflate
Connection: keep-alive
Host: localhost:8983
User-Agent: HTTPie/0.9.4



HTTP/1.1 400 Bad Request
Cache-Control: no-cache, no-store
Content-Length: 282
Content-Type: application/json; charset=UTF-8
ETag: "1605105208b"
Expires: Sat, 01 Jan 2000 01:00:00 GMT
Last-Modified: Wed, 13 Dec 2017 17:56:18 GMT
Pragma: no-cache

{
    "error": {
        "code": 400,
        "metadata": [
            "error-class",
            "org.apache.solr.common.SolrException",
            "root-error-class",
            "org.apache.solr.common.SolrException"
        ],
        "msg": "undefined field bla"
    },
    "responseHeader": {
        "QTime": 0,
        "params": {
            "q": "bla:*",
            "rows": "1",
            "wt": "json"
        },
        "status": 400,
        "zkConnected": true
    }
}