Minimal wx.FileDialog example freezes program

Question

I'm writing a new application.

I used to work with python 2.x and wxPython some years ago, now I got Python 3.7.0 and wxPythonPhoenix 4.0.4 msw (alas).

When I try to use wx.FileDialog with ShowModal, the program freezes.

I did not find any previous question about this. I used (and reduced for the MWE) code from wxWiki like this.

import wx

class MyFrame(wx.Frame):
    def __init__(self, parent, ID, title):
        wx.Frame.__init__(self, parent, ID, title, size=(400, 200))
        fileMenu = wx.Menu()
        openItem = fileMenu.Append(-1, "&Open...\tCtrl-O", "Open a new recipe")
        menuBar = wx.MenuBar()
        menuBar.Append(fileMenu, "&File")
        self.SetMenuBar(menuBar)
        self.Bind(wx.EVT_MENU, self.OnOpen, openItem)
    def OnOpen(self, event):
        # otherwise ask the user what new file to open
        with wx.FileDialog(self, "Open XYZ file", wildcard="XYZ files (*.xyz)|*.xyz",
                           style=wx.FD_OPEN | wx.FD_FILE_MUST_EXIST) as fileDialog:

            if fileDialog.ShowModal() == wx.ID_CANCEL:
                return     # the user changed their mind

        #you'll never get here      

app = wx.App()
frame = MyFrame(None, -1, "test")
frame.Show()
app.MainLoop()

I really don't get it, moreover the code actually worked for a couple of times.