text index with multi-key prefix is not rejected

> db.a.find() > db.a.createIndex({'x.name':'text'}) { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.a.insert({i:1, x:[{name:'pet', language:'en'}, {name:'animal domestique', language:'fr'}]}) WriteResult({ "nInserted" : 1 }) > db.a.insert({i:1, x:[{name:'fart', language:'en'}, {name:'pet', language:'fr'}]}) WriteResult({ "nInserted" : 1 }) > db.a.insert({i:1, x:[{name:'wax', language:'en'}, {name:'farter', language:'fr'}]}) WriteResult({ "nInserted" : 1 }) > db.a.find({$text:{$search:'fart', $language:'fr'}, 'x.language':'fr'}) { "_id" : ObjectId("584868134fb941395745c6bb"), "i" : 1, "x" : [ { "name" : "wax", "language" : "en" }, { "name" : "farter", "language" : "fr" } ] } { "_id" : ObjectId("584867ec4fb941395745c6ba"), "i" : 1, "x" : [ { "name" : "fart", "language" : "en" }, { "name" : "pet", "language" : "fr" } ] } > db.a.dropIndexes() > db.a.createIndex({'x.language':1, 'x.name': 'text'}) > db.a.find({'x.language':'fr', $text:{$search: 'fart', $language:'fr'}}) > db.a.find({'x.language':'fr', $text:{$search: 'fart', $language:'en'}}) > db.a.find({'x.language':'en', $text:{$search: 'fart', $language:'en'}}) // empty results