When I try fetch many big entities from cursor, it's return less than it has.
When I fetch not so match big entities, or small entities, cursor work correctly.
The more memory the object occupies, the less its returns cursor.
Maybe cursor have memory limit. And if entities summary size more than it limit, cursor return not all entities.

Mongo version 1.4.3

Examples:
> var cursor = db.test_coll.find().skip(0).limit(400).toArray();
> cursor.length;
289

But I have more than 289 entities:
> var cursor = db.test_coll.find().skip(0).limit(400);
> cursor.count(true);
400
> var cursor = db.test_coll.find().skip(400).limit(100).toArray();
> cursor.length;
100
> var cursor = db.test_coll.find().skip(400).limit(400).toArray();
> cursor.length;
283

If I run query witout limit, cursor return less entities:
> var cursor = db.test_coll.find().toArray();
> cursor.length;
71
> var cursor = db.test_coll.find();
> cursor.count(true);
835

It problem I have in mongo console and in PHP API:
$data = $mongo_collection_handler->find(array())>skip(0)>limit(400);
echo $data->count(true); // return 835
$counter = 0;
foreach ($data as $value){
$counter++;
}
echo $counter; // return 289