Stop words not working when setting analyzer in settings

I'm trying to change the haystack default settings to something very simple:

   'settings': {
            "analyzer": "spanish"
    }

It looks right after rebuilding the index:

$ curl -XGET 'http://localhost:9200/haystack/_settings?pretty=true'
{
"haystack" : {
"settings" : {
"index.analyzer" : "spanish",
"index.number_of_shards" : "5",
"index.number_of_replicas" : "1",
"index.version.created" : "191199"
}
}

But when testing it with some stop words it won't work as expected (it
should filter out "esto" and "que"):

$ curl -XGET
'localhost:9200/haystack/_analyze?text=esto+is+a+test+que&pretty=true'
{
"tokens" : [ {
"token" : "esto",
"start_offset" : 0,
"end_offset" : 4,
"type" : "",
"position" : 1
}, {
"token" : "test",
"start_offset" : 10,
"end_offset" : 14,
"type" : "",
"position" : 4
}, {
"token" : "que",
"start_offset" : 15,
"end_offset" : 18,
"type" : "",
"position" : 5
} ]

And only when I specify the analyzer in the query it works:

$ curl -XGET
'localhost:9200/haystack/_analyze?text=esto+is+a+test+que&analyzer=spanish&pretty=true'
{
"tokens" : [ {
"token" : "is",
"start_offset" : 5,
"end_offset" : 7,
"type" : "",
"position" : 2
}, {
"token" : "test",
"start_offset" : 10,
"end_offset" : 14,
"type" : "",
"position" : 4
} ]

Any idea of what am I doing wrong?

Thanks.

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