You might have to derive a new class from QCalendarWidget and override some of the mouse handling. My guess is that the widget eats the mouse events and converts them into the other signals.
For starters, you could implement an event filter then use the debugger to see what happens in response to the mousePresseEvent and mouseReleaseEvent events. I imagine a complex widget like this could be pretty easy to break if you start adding custom handling for events.
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