I create document via emongo driver:

emongo:insert(database, "my_collection", [

{x,4}

,

{x,1}

,

{x,3}

]).

Now I select it:

emongo:find_all(database, "my_collection").

[[{<<"_id">>,
{oid,<<80,156,252,176,8,197,245,106,230,82,14,180>>}},

{<<"x">>,4}

,

{<<"x">>,1}

,

{<<"x">>,3}

]]

Now I go to console:

mongo database
> > db.t.find()

{ "_id" : ObjectId("509cfcb008c5f56ae6520eb4"), "x" : 4, "x" : 4, "x" : 4 }

I see here two problems:
1) I can store document with many instances of key and search is done only via first instance of key
2) mongo console doesn't understand it and looses other values for this key