FacetField-Result on String-Field contains value with count 0?

[Sebastian Riemer]

Hi,

Please help me understand: 
http://localhost:8983/solr/wemi/select?facet.field=m_mediaType_s&facet=on&indent=on&q=*:*&wt=json
 returns:

"facet_counts":{
    "facet_queries":{},
    "facet_fields":{
      "m_mediaType_s":[
        "2",25561,
        "3",19027,
        "10",1966,
        "11",1705,
        "12",1067,
        "4",1056,
        "5",291,
        "8",68,
        "13",2,
        "6",2,
        "7",1,
        "9",1,
        "1",0]},
    "facet_ranges":{},
    "facet_intervals":{},
    "facet_heatmaps":{}}}

http://localhost:8983/solr/wemi/select?fq=m_mediaType_s:%222%22&indent=on&q=*:*&rows=0&start=0&wt=json


?  "response":{"numFound":25561,"start":0,"docs":[]

http://localhost:8983/solr/wemi/select?fq=m_mediaType_s:%220%22&indent=on&q=*:*&rows=0&start=0&wt=json


?  "response":{"numFound":0,"start":0,"docs":[]

So why does the search for facet.field even contain the value "1", if it does 
not exist?

And why does it e.g. not contain 
"SomeReallyCrazyOtherValueWhichLikeValue"1"DoesNotExistButLetsIncludeItInTheFacetFieldsResultListAnywaysWithCountZero"
 : 0

Best regards,
Sebastian

Additional info, field m_mediaType_s is a string;
<dynamicField name="*_s"     type="string"                   indexed="true"  
stored="true" />
<fieldType name="string" class="solr.StrField" sortMissingLast="true" />