MongoDB $or issues

> db.foo.insert({a: {john: true, george: true}})
> db.foo.insert({a: {paul: true, ringo: true}})
> db.foo.find()
{ "_id" : ObjectId("4d43912ceb913a1024b1410f"), "a" : { "john" : true, "george" : true } }
{ "_id" : ObjectId("4d43914beb913a1024b14110"), "a" : { "paul" : true, "ringo" : true } }

> db.foo.find({'a.john': {$exists: true}})
{ "_id" : ObjectId("4d43912ceb913a1024b1410f"), "a" : { "john" : true, "george" : true } }

> db.foo.find({'a.paul': {$exists: true}})                                      
{ "_id" : ObjectId("4d43914beb913a1024b14110"), "a" : { "paul" : true, "ringo" : true } }

> db.foo.find({$or: [{'a.john': {$exists: true}}, {'a.paul': {$exists: true}}]})
> 

> db.foo.stats()
{
	"ns" : "topher_test.foo",
	"count" : 2,
	"size" : 96,
	"storageSize" : 2816,
	"numExtents" : 1,
	"nindexes" : 1,
	"lastExtentSize" : 2816,
	"paddingFactor" : 1,
	"flags" : 1,
	"totalIndexSize" : 8192,
	"indexSizes" : {
		"_id_" : 8192
	},
	"ok" : 1
}

db.foo.find({$or: [{'a.john': {$exists: true}}, {'a.paul': {$exists: true}}]})
{ "_id" : ObjectId("4d4392e753ffe3441923319b"), "a" : { "john" : true, "george" : true } }
{ "_id" : ObjectId("4d4392f053ffe3441923319c"), "a" : { "paul" : true, "ringo" : true } }

Turns out the issue with $or not working is that I was using an old version released prior to the introduction of $or.