Kibana filters running as ES Queries

Running Kibana 5-alpha5, in the Discover tab when you add a filter to your search (for example, by clicking the + sign next to a field), it filters out the results according to that value, but looking at the request that is actually being sent to the server shows that Kibana doesn't add an Elasticsearch filter, but it adds a match query instead. Why is that? Since filtering on an field means exact matching it, wouldn't it be beneficial to run it as a filter?