Data in collection compact_channel_data record:
{
    "_id" : ObjectId("562786dc99d0948a7f1fb3de"),
    "channel_name" : "NPr-1.1",
    "valid" : true,
    "data" : [
        {
            "ieq_input_raw_value" : "010010000000000000000000000000000000000000000000",
            "sensor_datetime" : 1445429500.625,
            "db_datetime" : ISODate("2015-10-21T14:11:40.625Z")
        },
        {
            "ieq_input_raw_value" : "110010000000001000000000000000000000000000000000",
            "sensor_datetime" : 1445429500.66,
            "db_datetime" : ISODate("2015-10-21T14:11:40.660Z")
        },
        {
            "ieq_input_raw_value" : "110010000000001001001000000000000000000000000000",
            "sensor_datetime" : 1445429500.624,
            "db_datetime" : ISODate("2015-10-21T14:11:40.624Z")
        },
        {
            "ieq_input_raw_value" : "110010000000001011001000000000100000000000000000",
            "sensor_datetime" : 1445429500.659,
            "db_datetime" : ISODate("2015-10-21T14:11:40.659Z")
        },
        {
            "ieq_input_raw_value" : "110010000000001010001000000000100000000000000000",
            "sensor_datetime" : 1445429500.671,
            "db_datetime" : ISODate("2015-10-21T14:11:40.671Z")
        },
        {
            "ieq_input_raw_value" : "110010000000001010001000000001100000000000000000",
            "sensor_datetime" : 1445429500.679,
            "db_datetime" : ISODate("2015-10-21T14:11:40.679Z")
        }
    ],
    "device_id" : ObjectId("560e197f99d094dea7023768")
}

If I execute following query:
db.compact_channel_data.find({},{'data.sensor_datetime': 1}).sort({'data.sensor_datetime': 1})

I receive following result:
/* 0 */
{
    "_id" : ObjectId("562786dc99d0948a7f1fb3de"),
    "data" : [
        {
            "sensor_datetime" : 1445429500.625
        },
        {
            "sensor_datetime" : 1445429500.66
        },
        {
            "sensor_datetime" : 1445429500.624
        },
        {
            "sensor_datetime" : 1445429500.659
        },
        {
            "sensor_datetime" : 1445429500.671
        },
        {
            "sensor_datetime" : 1445429500.679
        }
    ]
}

But there is problem because the value 1445429500.66 should be behind 1445429500.659.

The original value of 1445429500.66 (ISODate("2015-10-21T14:11:40.660Z") shall be behind 1445429500.659 ISODate("2015-10-21T14:11:40.659Z").