After connecting to *.accdb file with pyodbc, I cannot type Korean language in QLineEdit

(Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 16:07:46) [MSC v.1900 32 bit (Intel)] on win32)

I'm trying to make a program using pyqt5 and pyodbc.

There are some QLineEdit widgets and QPushButton widgets in a QMainWindow. I wrote a function that connects to accdb file. The function(slot) is connected to a button.

Everything worked fine. I could connect to accdb file and get datas from there. But I found if I type Korean character(Hangul) in QLineEdit, the program stops with exit code -1073741819 (0xC0000005).

Strange thing is that if I call the function in __init__(self) it works fine with no error. But if I call the function by clicking the button, although the code works, typing Korean characters makes the program stop. (Latin characters are OK.)

Similar code worked fine when I used mysql.connector with Maria DB instead of pyodbc. But I have no choice but using accdb file so I tried pyodbc.

code1 below works fine. I can type every characters in QLineEdit widgets.

    form_class_main = uic.loadUiType("UI.ui")[0]
    class Form_Main(QMainWindow, form_class_main):
        def __init__(self):
            super().__init__()
            self.setupUi(self)
            self.test1()

    def test1(self):
        cnx = pyodbc.connect(connStr)
        cnx.close()
        print("OK")

code2 below also works fine, before I try to type Korean in QLineEdit widgets.

    form_class_main = uic.loadUiType("UI.ui")[0]
    class Form_Main(QMainWindow, form_class_main):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.btn1.clicked.connect(self.test1)

    def test1(self):
        cnx = pyodbc.connect(connStr)
        cnx.close()
        print("OK")

with this code above, If I can type Korean characters in QLineEdit before I click btn1. After clicking the button, (I can do whatever I want but) as soon as I try to type Korean characters in QLineEdit widgets, the program stops.

How could I solve this problem? If there is no solution, is there other way to replace pyodbc?