Mongoose deleting (pull) a document within an array, does not work with ObjectID

I have the following mongoose schema:

user = {
    "userId" : "myId",
    "connections":
    [{
        "dateConnectedUnix": 1334567891,
        "isActive": true
    }, {
        "dateConnectedUnix": 1334567893,
        "isActive": false
    }]
}

I would like to delete the second item in the connections array, to get the following:

user = {
    "userId" : "myId",
    "connections": 
    [{
        "dateConnectedUnix": 1334567893,
        "isActive": false
    }]
}

The following code does the job as expected:

userAccounts.update(
    { 'connections.isActive': false }, 
    { $pull: { 'connections.isActive':false }}, 
    function (err, val) {
        console.log(val)
    }
);

But, I need to delete based on ObjectId. And the following goes does not work:

userAccounts.update(
    { 'connections._id': '1234-someId-6789' }, 
    { $pull: { 'connections._id': '1234-someId-6789' } },
    function (err, val) {
        console.log(val)
    }
);

Any suggestions? I have been banging my head against the screen (aka Google, Stackoverflow, ...) for hours and have had no luck.

It seems that the above code would not work. It should not even have worked for the first example I gave.

In the end I was supported by this answer here: MongoDB, remove object from array

Here is my working code:

userAccounts.update( 
    { userId: usr.userId },
    {
        $pull: {
            connections: { _id : connId }
        }
    },
    { safe: true },
    function removeConnectionsCB(err, obj) {
        // ...
    }
);