View Engine not detecting meta.id if doc has xattrs

Tested on build 5.0.0-2109 and 5.0.0-2140
The following simple view does not emit documents containing xattrs:

function (doc, meta) {

  emit(meta.id, null);

}

e.g. if I have 3 docs in my cluster, 2 of which don't contain xattrs and 1 which contains xattrs, the view will only yield 2 rows. If I modify the view slightly to (for example):

function (doc, meta) {

  emit(doc.name, meta.id);

}

Then all 3 documents are returned by the view and meta.id is displayed correctly for all three documents.