PyQt Linux Segfaults on QPushbutton::text()

I can repeatedly (but not consistently) generate segfaults on linux with PyQt4 and PyQt5 but running tests which use `ModalDialogTester.click_widget` (or `ModalDialogTester.click_button`). For example, running the confirmation dialog test suite a few times will segfault > 50% of the time.

Tracing the fault, the immediate cause while is that while walking the dialog's buttons, asking for their `text()` can cause the segfault. It is unclear what causes the problem. It could potentially be:

- incomplete set-up (unlikely, when catching with gdb dialogs look to be complete)
- custom button text which has been garbage collected (failures do appear to occur in tests which don't change tests, however)
- a bug in Qt, PyQt, or the EDM builds thereof (this is the most likely)