Field collapsing, facets, and qtime: caching issue?

[Ronald K. Braun]

I'm experimenting with field collapsing in solrcloud 6.2.1 and have this
set of request parameters against a collection:

/default?indent=on&q=*:*&wt=json&fq={!collapse+field=groupid}

My default handler is just defaults:

    <requestHandler name="/default" class="solr.SearchHandler">
        <lst name="defaults">
            <str name="echoParams">explicit</str>
        </lst>
    </requestHandler>

The first query runs about 600ms, then subsequent repeats of the same query
are 0-5ms for qTime, which I interpret to mean that the query is cached
after the first hit.  All as expected.

However, if I enable facets without actually requesting a facet:

/default?indent=on&q=*:*&wt=json&fq={!collapse+field=groupid}&facet=true

then every submission of the query runs at ~600ms.  I interpret this to
mean that caching is somehow defeated when facet processing is set.  Facets
are empty as expected:

    facet_counts": {
      "facet_queries": { },
      "facet_fields": { },
      "facet_ranges": { },
      "facet_intervals": { },
      "facet_heatmaps": { }
    }

If I remove the collapse directive

/default?indent=on&q=*:*&wt=json&facet=true

qTimes are back down to 0 after the initial query whether or not faceting
is requested.

Is this expected behaviour or am I missing some supporting configuration
for proper field collapsing?

Thanks!

Ron