Shard query cache and filters with _cache:false

Is the shard query cache disabled if a filter is specified in query.filter.filtered.bool.must clause has _cache: false? It makes some intuitive sense if it's the case, but looking over the source code (we're using 1.4.3), I can't see any reason why this would happen yet it seems to on most of our queries (confirmed it's enabled in our settings at 2% of heap).