Status bar in a task application not visible unless window is resized

(With pyface 6.0.0-1, qt4, python 3)
I have added a `status_bar` to a pyface `Task` however by default it is not visible until the user resizes the window vertically. This can be seen by adding a line like `status_bar = StatusBarManager()` to the example task in the advanced tasks examples.

Here is what the window looks like in the example (I have closed the dock pane as not relevant):

Here is what the window looks like after resizing (note the status bar at the bottom, which now stays visible regardless of resizing):