So I have looked further and found that the event() function in QWidget is not virtual, which I'm not sure why that's that way.
That is not true - its virtual protected:
(documentation):
bool QWidget::event ( QEvent * event ) [virtual protected]
This is not realated (that I can see) to the problem you are talking about but:
Qt Code: 
  1. installEventFilter(this);
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This code makes no sense.
You use an event filter when you want anotehr object to filter this objects events - each object receives its own events any way.

Why do you use Q_UNUSED when you are clearly using the variable?

At the moment I don't see why some events will not be caught in your event() handler, in respect to your original post (except that the code for these events is not in the function as you are now using the specialized handlers).