pyqt5, tvtk SceneModel pane not moving in some traitsui views

In two cases, firstly when using an (traitsui) InstanceEditor on a class inheriting from SceneModel. See minimal example:

```
from tvtk.pyface.scene_model import SceneModel
from tvtk.pyface.scene_editor import SceneEditor
from tvtk.api import tvtk
​
from traits.api import Button, HasStrictTraits, Instance, Int, Property
​
from traitsui.api import UItem, View, InstanceEditor
​
# %%
​
​
class InheritedScene(SceneModel):
​
#: someone tell me how put self as an UItem
self_scene = Property()
​
def _get_self_scene(self):
return self
​
test_view = View(
UItem('self_scene', editor=SceneEditor())
)
​
​
class TestSceneViewer(HasStrictTraits):
​
test_scene = Instance(InheritedScene, ())
​
view = View(
UItem('test_scene', style='custom',
editor=InstanceEditor(view='test_view')),
resizable=True
)
​
​
test_scene_viewer = TestSceneViewer()
test_scene_viewer.test_scene.configure_traits(view='test_view') # fine
test_scene_viewer.configure_traits(view='view') # broken
```

And the second (more important case) is the toolbar is not moving when I drag the window around when I embed it within a VSplit/HSplit (it works fine with Groups tho). See the minimal example below:

```
from traits.api import Button, HasStrictTraits, Instance
​
from traitsui.api import UItem, VSplit, View
​
from tvtk.pyface.scene_editor import SceneEditor
from tvtk.pyface.scene_model import SceneModel
​
​
class TestSceneViewer(HasStrictTraits):
​
test_scene = Instance(SceneModel, ())
​
create_arrow = Button()
​
view = View(
VSplit(
UItem('test_scene', editor=SceneEditor()),
UItem('create_arrow'),
),
resizable=True
)
​
​
this_scene = SceneModel()
test_scene_viewer = TestSceneViewer(test_scene=this_scene)
test_scene_viewer.configure_traits()
```