It seems that the Blinker library (https://pythonhosted.org/blinker/) uses weak references.
Hi there! Have you found the solution? I’ve experienced the exact same problem per your description. Your conclusion is on point. For my case of “deep hierarchy of components”, a quick print(self.parent.parent.parent.parent.parent) proves that. Apparently, it does bubble up but couldn’t reach my top-most form named Booking(). So, I got my code working by using: self.data_grid_1.set_event_handler(“x-check-in-time-selected”, self.check_in_time_selected) instead of: self.set_event_handler(“x-check-in-time-selected”, self.check_in_time_selected) in my top-most form.