Certain queries against compound 2d/text indexes are incorrectly covered, return incorrect results

> db.foo.drop() true > db.foo.insert({a: 1, "location" : [ -117.15, 32.88 ]}) WriteResult({ "nInserted" : 1 }) > db.foo.insert({a: 2, "location" : [ -117.15, 32.88 ]}) WriteResult({ "nInserted" : 1 }) > db.foo.insert({a: 3, "location" : [ -117.15, 32.88 ]}) WriteResult({ "nInserted" : 1 }) > db.foo.ensureIndex({location: "2d"}) { "createdCollectionAutomatically" : false, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } In the query below, we request documents where b exists. As expected, we get 0 results. > db.foo.find({location: { $nearSphere: [ -117.2684194, 33.1029176 ], $maxDistance: 0.02526017985248055 }, b: { $exists: true}}) # no results (expected) When an index is added on (location, b), all documents are returned when $exists: true is set for b, which is incorrect. > db.foo.ensureIndex({location: "2d", b: 1}) { "createdCollectionAutomatically" : false, "numIndexesBefore" : 2, "numIndexesAfter" : 3, "ok" : 1 } > db.foo.find({location: { $nearSphere: [ -117.2684194, 33.1029176 ], $maxDistance: 0.02526017985248055 }, b: { $exists: true}}).hint("location_2d_b_1") { "_id" : ObjectId("562524f65a47d987934ec69b"), "a" : 1, "location" : [ -117.15, 32.88 ] } { "_id" : ObjectId("562524fb5a47d987934ec69c"), "a" : 2, "location" : [ -117.15, 32.88 ] } { "_id" : ObjectId("562525005a47d987934ec69d"), "a" : 3, "location" : [ -117.15, 32.88 ] }