The Pose FK mode assings the rotation origin to the boundary of the last visited face set in the floodfill operation. In some cases, the topology of the model may make the flood fill operation to visit a face set as the first one (assinging it to target) and visit it again as the last one (assinging it to origin). This will make the pose brush to default the origin and target to the brush location and not to the face sets as it considers that there is only one possible boundary. This adds a GSet to ensure that a particular face set is not visited twice in the flood fill, fixing these cases. Reviewed By: sergey Differential Revision: https://developer.blender.org/D7984