Union is reducing number of vertices

Hi! I'm using rbclipper to make the union of 2 polygons. The result is one polygon that seems to be the union of both, but the result looks... simplified. The number of vertices seem to be reduced, and hence the original shape of both polygons is not maintained.

Following is a picture of both polygons and the result

As you can see, the picture on the right seems to be the union, but borders don't have the detail of the original polygons.