With a pie chart each slice is a region. When you have them set with PickOnBounds see RT-22954. Then move the mouse over the slices, you see odd slices highlighted when the mouse is in middle of a slice.

If you run the attached app and put the cursor somewhere along the lines (305, 116) -> (375, 116) , (305, 148) -> (375, 148) or (300, 120) -> (300, 260), the wrong Node will be picked.