Issues with refine parameter when subfaceting in a range facet

[Tom Van Cuyck]

Hi,

We encountered an issue when using the refine parameter when subfaceting in
a range facet.
When enabling the refine option, the counts of the response are the double
of the counts of the response without refine option.
We are running Solr 6.6.1 in a cloud setup.

If I execute the query:

curl http://localhost:8899/solr/data/select -d '{ "params" :
{"wt":"json","rows":0,"json.facet":"
  {

    \"MaximumAge_f\":
    {
      \"type\":\"range\",
      \"field\":\"MaximumAge_f\",
      \"start\":0.0,
      \"end\":55000.0,
      \"gap\":1000.0,
      \"other\":\"between\",
      \"facet\":
      {
        \"Gender_sf\":
        {
          \"type\":\"terms\",
          \"field\":\"Gender_sf\",
          \"missing\":true,
*          \"refine\":true,*
          \"overrequest\":24,
          \"limit\":12,
          \"offset\":0
        }
      }
    }
  }",
  "q":"*:*"
}'

I get the following response:

  "facets": {
    "count": 379417,
    "MaximumAge_f": {
      "buckets": [
        {
          "val": 0,
          "count": 8252,
          "Gender_sf": {
            "buckets": [
              {
                "val": "All",
                "count": 8152
              },
              {
                "val": "Male",
                "count": 74
      {
              },
              {:wink
                "val": "Female",
                "count": 26
              }
            ],
            "missing": {
              "count": 0
            }
          }
        },
...

If I execute the same query WITHOUT refine: true in the subfacet, I get the
following response:

  "facets": {
    "count": 379417,
    "MaximumAge_f": {
      "buckets": [
        {
          "val": 0,
          "count": 4126,
          "Gender_sf": {
            "buckets": [
              {
                "val": "All",
                "count": 4076
              },
              {
                "val": "Male",
                "count": 37
              },
              {
                "val": "Female",
                "count": 13
              }
            ],
            "missing": {
              "count": 0
            }
          }
        },
...

There is a factor 2 difference for each count in each bucket.

If I perform the same queries with a larger range gap, e.g.
      \"start\":0.0,
      \"end\":55000.0,
      \"gap\":5000.0,
there is no difference between the response with and without refine: true.

Is this a known issue, or is there something we are overlooking?
And is there information on whether or not this behavior will be the same
in Solr 7?

Kind regards, Tom