MySQL pipelined order by seems not working - mysql

Question

I have table
user[id, name, status] with index[status, name, id]
SELECT *
FROM user
WHERE status = 'active'
ORDER BY name, id
LIMIT 50
I have about 50000 users with status == 'active'
1.) Why does MySQL explain show about 50000 in ROWS column? Why it follows all leaf nodes even when the index columns equals to order by clause?
2.) When I change order by clause to
ORDER BY status, name, id
EXTRA column of explain clause shows:
Using index condition; Using where; Using filesort
Is there any reason why it can't use index order in this query?
edit1:
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`status` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `status_name_id` (`status`,`name`,`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
query:
SELECT *
FROM `user`
WHERE status = 'complete'
ORDER BY status, name, id
LIMIT 50
explain:
id: 1
select_type: SIMPLE
table: f_order
type: ref
possible_keys: status_name_id
key: status_name_id
key_len: 768
ref: const
rows: 50331
Extra: "Using where; Using index; Using filesort"
The weirdest thing is that if I change SELECT statement to
SELECT *, count(id)
It use index again and query is twice faster. And extra section contains only
Using where; Using index
Table contains 100k rows, 5 different statuses and 12 different names.
MySQL: 5.6.27
edit2:
Another example:
This takes 400ms (avg) and does explicit sort
SELECT *
FROM `user`
WHERE status IN('complete')
ORDER BY status, name, id
LIMIT 50
This takes 2ms (avg) and doesn't explicit sort
SELECT *
FROM `user`
WHERE status IN('complete', 'something else')
ORDER BY status, name, id
LIMIT 50

Answer 1

Q1: EXPLAIN is a bit lame. It fails to take into account the existence of the LIMIT when providing the Rows estimation. Be assured that if it can stop short, it will.
Q2: Did it say that it was using your index? Please provide the full EXPLAIN and SHOW CREATE TABLE.
More
With INDEX(status, name, id), the WHERE, ORDER BY, and LIMIT can be handled in the index. Hence it has to read only 50 rows.
Without that index, (or with practically any change to the query), much or all of the table would need to be read, stored in a tmp table, sorted, and only then could 50 rows be peeled off.
So, I suggest that it is more complicated than "explicit sort can kill my db server".

Answer 2

According to comments it is probably bug.