Found this on Qt Bug Tracker. Do a search for setCursor. There seem to be a lot of bugs related to it.
I ginned up a C++ version of your app and tried setting the cursor on the viewport as suggested in the first comment, but it didn't completely work either. And I'm using 4.7.0-beta1. It works okay if the cursor is not over one of the graphicsitems when F1||F2||F3 is pressed and then moved onto an item, but not the other way round. The view always retains its last setting if a button is pressed while the cursor is over an item.
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