SUM() counts row twice and displaying double result - mysql

Question

Why SUM() counts row twice and displaying double of actual result in here ?
Here I m trying to count total rows of status that has 0 value from the inv_id table of each student (inv_id.s_id) .
it has to show 4 based on the row number in inv_lst table but here it is showing 8.
If fee.id is GROUP_BY then it shows actual SUM but same student id starts to duplicate.
Please see fiddle - SQL Fiddle
Database Structure
class
id | ttl
===========
1 | One
2 | Two
section
id | ttl
===========
1 | A
2 | B
fee
id | ttl
===============
1 | Annual
2 | Monthly
student
id | ttl | cls | sec
===========================
1 | John| 1 | 1
2 | Paul| 1 | 1
3 | Rina| 2 | 1
sec_fee
id | c_id| s_id| f_id| fee
===================================
1 | 1 | 1 | 1 | 1000
2 | 2 | 1 | 2 | 560
inv_id
id | s_id| ft_id | status
==================================
1 | 1 | 1 | 0
2 | 1 | 2 | 0
3 | 1 | 3 | 0
4 | 1 | 4 | 0
Mysql
SELECT
student.id, student.ttl AS stdt,
cls.ttl AS cls,
sec.ttl AS sec,
GROUP_CONCAT(DISTINCT fee.id, '.', fee.ttl, '-', sec_fee.fee,'<br/>' ORDER BY sec_fee.f_id) AS amnt,
SUM(inv_id.status=0) AS upad,
SUM(inv_id.status=1) AS pad
FROM
student
JOIN
cls ON cls.id=student.cls
LEFT JOIN
sec ON sec.id=student.sec
LEFT JOIN
inv_id ON inv_id.s_id = student.id
LEFT JOIN
sec_fee ON sec_fee.c_id = student.cls
LEFT JOIN
fee ON fee.id = sec_fee.f_id
WHERE
cls.id = 1