Run PySide GUI app inside Photoscan

[mixa]

Hi. I try to run PySide GUI inside Photoscan, menu is added, but when i try to run script from menu, GUI show and after close automatically.
mainForm.exec() works, but i need to open this widget in non modal mode.

from PySide.QtCore import *
from PySide.QtGui import *


class MainForm(QDialog):

    def __init__(self):
        QDialog.__init__(self, None)
        self.setWindowTitle("Hello")


def main():

    app = QCoreApplication.instance()

    if app == None:
        app = QApplication([])

    mainForm = MainForm()
    mainForm.show()
    # mainForm.exec()

PhotoScan.app.addMenuItem("TestMenu/TestScript", main)