Query not returning correct total

Regarding the second practice (User loans), I wrote a query (see below) that shows for any patron the open loans in the south and north + a total of both.

This functions perfectly fine for all patrons BUT patron 4. Patron 4 does have a value in the OpenLoansS column but a NULL in the OpenLoansN column. The TotalOpenLoans column becomes NULL. Could someone please help me figure out why?

QUERY (feel free to copy+paste):

SELECT p.id, p.first_name, NRsouth.OpenLoans AS OpenLoansS, NRnorth.OpenLoans AS OpenLoansN, NRsouth.OpenLoans + NRnorth.OpenLoans AS TotalOpenLoans FROM patrons AS p LEFT OUTER JOIN ( SELECT patron_id, COUNT() AS OpenLoans FROM loans_south WHERE returned_on IS NULL GROUP BY patron_id ) AS NRsouth ON NRsouth.patron_id = p.id LEFT OUTER JOIN ( SELECT patron_id, COUNT() AS OpenLoans FROM loans_north WHERE returned_on IS NULL GROUP BY patron_id ) AS NRnorth ON NRnorth.patron_id = p.id GROUP BY p.id;

RETURNED SET:

id / first_name / OpenLoansS / OpenLoansN / TotalOpenLoans;

1 / Andrew / 6 / 4 / 10

2 / Dave / 2 / 5 / 7

3 / Alena / 4 / 4 / 8

4 / Michael / 3 / NULL / NULL

5 / Craig / NULL / NULL / NULL