Title bar captured incorrectly after changing window width

from PySide6.QtCore import QTimer
from PySide6.QtWidgets import QApplication, QMainWindow

application = QApplication()
window = QMainWindow()
window.show()
screen = window.screen()

def save_titlebar(filename: str) -> None:
    window.screen().grabWindow(
        window.winId(),
        x=window.frameGeometry().x() - window.geometry().x(),
        y=window.frameGeometry().y() - window.geometry().y(),
        w=window.frameGeometry().width(),
        h=window.frameGeometry().height() - window.geometry().height(),
    ).save(filename)

def set_width_and_save(width: int) -> None:
    window.setFixedWidth(width)
    QTimer.singleShot(500, lambda: save_titlebar(f"titlebar{width}.png"))

QTimer.singleShot(1000, lambda: set_width_and_save(400))
QTimer.singleShot(2000, lambda: set_width_and_save(500))
QTimer.singleShot(3000, lambda: set_width_and_save(300))
QTimer.singleShot(4000, window.close)
application.exec()