Rasperry Pi loses Mysql Connection?

Question

I am trying to insert data into a mysql database with a keypad connected to a Rasperry PI using python.

The code:

#!/usr/bin/python

import os
import MySQLdb
import RPi.GPIO as GPIO
import time

#Open db conn
db = MySQLdb.connect("remote_server.com","user","password","database")

# prep cursor
cursor = db.cursor()

GPIO.setmode(GPIO.BOARD)
MATRIX = [      [1,2,3],
            [4,5,6],
            [7,8,9],
            ['*',0,'#']     ]

ROW = [7,11,13,15]
COL = [23,21,19]

for j in range(3):
    GPIO.setup(COL[j], GPIO.OUT)
    GPIO.output(COL[j], 1)

for i in range(4):
    GPIO.setup(ROW[i], GPIO.IN, pull_up_down = GPIO.PUD_UP)

try:
    while(True):
            for j in range(3):
                    GPIO.output(COL[j],0)
                    for i in range(4):
                            if GPIO.input(ROW[i]) == 0:
                                    mysql_code = MATRIX[i][j]
                                    print mysql_code
                                    try:
                                            cursor.execute('''Insert into Rasperry_Codes (Code, insertTS) VALUES (%s, NOW())''', (mysql_code))
                                    except MySQLdb.Error, e:
                                            try:
                                                    print "MySQL Error [%d]: %s" % (e.args[0], e.args[1])
                                            except IndexError:
                                                    print "MySQL Error: %s" % str(e)

                                    db.commit()
                                    time.sleep(0.2)
                                    while(GPIO.input(ROW[i]) == 0):
                                            pass

                    GPIO.output(COL[j],1)
except KeyboardInterrupt:
    GPIO.cleanup()

Sometimes the data is inserted into database, sometimes not.

No error is given from mysql MySQLdb.Error.

print mysql_code always prints the correct pressed number.

Does anybody see a problem that could cause that random malfunction?