QDateEdit bug

I have noticed that there is a bug in QDateEdit widget, I am using Qt Designer 5.15.2 to design QPushButton, QDateEdit and QLineEdit with python 3.9.2:

Code:

---

from PyQt5.QtWidgets import *
from PyQt5.uic import loadUiType
import sys
Ui_MainWindow,_ = loadUiType('tst.ui')
class TEST(Ui_MainWindow, QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)
        self.setupUi(self)
        self.btn.clicked.connect(self.enterDATE) #QPushButton signal
    def enterDATE(self):
        Date_2021_03_26 = "{0}-{1}-{2}".format(self.deDateEdit.date().year(), self.deDateEdit.date().month(), self.deDateEdit.date().day()) #QDateEdit
        self.LineEdit.setText(Date_2021_03_26) #QLineEdit
def main():
    app = QApplication(sys.argv)
    win = TEST()
    win.show()
    app.exec_()
if __name__ == '__main__':
    main()

---

you will notice that when you try to type this specific date: 2021-03-26 by keyboard, it will be rejected (in my case it sat to 2021-03-01)
if you try other dates (try change the year, month and day) it will accept them. why this happened only for this date 2021-03-26?
note that: if you use the updown arrows to type(select) the date, it will accept the date 2021-03-26
I hope someone help me to understand the reason.

No issue here with Qt 5.12 and Python 3.8.5. Break for you?

Code:

---

from PyQt5.QtWidgets import *
from PyQt5.QtCore import QDate
import sys
 
class Widget(QWidget):
    def __init__(self):
        QWidget.__init__(self)
        self.dateEdit = QDateEdit()
        self.dateEdit.setDate(QDate(2021, 3, 1))
        self.dateEdit.setDisplayFormat("yyyy-MM-dd")
        self.lineEdit = QLineEdit(self)
        layout = QVBoxLayout(self)
        layout.addWidget(self.dateEdit)
        layout.addWidget(self.lineEdit)
        self.dateEdit.setFocus()
        self.dateEdit.dateChanged.connect(self.showDate)
 
    def showDate(self, date):
        dateString = "{0}-{1}-{2}".format(date.year(), date.month(), date.day())
        self.lineEdit.setText(dateString)
 
def main():
    app = QApplication(sys.argv)
    win = Widget()
    win.show()
    app.exec_()
 
if __name__ == '__main__':
    main()

---

my friend,, I tried your code.
if you changed self.dateEdit.setDate(QDate(2021, 3, 1)) to self.dateEdit.setDate(QDate(2021, 1, 1))
and tried to type 2021-03-26 , you will get a problem (bug)
I can't set date to 2021-03-01, because when you design an application, you will set the date to the default which is year/01/01 .