$elemMatch results not a subset of non $elemMatch results when there are missing values

> c.drop();
true
> c.save( {a:[

{b:1}

,{}]} )
> c.find(

{'a.b':null}

)
> c.find( {a:{$elemMatch:

{b:null}

}} )
{ "_id" : ObjectId("4e13d80b82517cd82873bc17"), "a" : [

{ "b" : 1 }

, { } ] }

Don't know if this is desired or not, thought I would check.

Also, the behavior is different from the above if the field missing 'b' is not an object:

> c.drop()
false
> c.save( {a:[

{b:1}

,'z']} )
> c.find(

{'a.b':null}

)
> c.find( {a:{$elemMatch:

{b:null}

}} )
>