When you apply a contour to an object, by default CorelDRAW will apply Mitered corners to it. There are two other options available to choose other than Mitered; Round and Bevel. When a contour object is selected, you will see button on property bar. Clicking on the button will reveal options to toggle between Mitered, Round or Bevel corners.
Tip provided by Pratik Shah, CorelDRAW Master, graphic designer
Great tip! But I think there was a mistake in the images that illustrate this tip. You are showing the options rectangle corners when it should show the effect contour corners.