@apw: I've tested the 5.5.1+dfsg-16ubuntu7.4 in xenial-proposed with the test case I attached in comment #4, as well as the Wrapping/Python/vtk/qt/QVTKRenderWindowInteractor.py script in the VTK source, and the problem is fixed.
@apw: I've tested the 5.5.1+dfsg- 16ubuntu7. 4 in xenial-proposed with the test case I attached in comment #4, as well as the Wrapping/ Python/ vtk/qt/ QVTKRenderWindo wInteractor. py script in the VTK source, and the problem is fixed.