Facet aggregation functions on date fields return numbers

When you use the JSON faceting API and you want to use aggregate functions on date fields, you get numbers instead.
e.g.

json.facet= {
"test": {"type": "query", "q": "*:*", "facet": {"first": "min(date)", "last": "max(date)"}}
}

Where date has a date type, you'll get

{"count":15, "first":1.361525185E12, "last":1.387552939E12}

It'd be nice to get the results in a standard TZ format.

Someone already described this issue here:
http://lucene.472066.n3.nabble.com/min-max-on-date-fields-using-JSON-facets-td4288736.html
But I haven't found any JIRA ticket linked to this problem.