Vector masking is cropping, not clipping. When you use a vector shape to mask another object, the cropping/masking shape becomes completely invisible. When you clip an object to a vector shape you create a ‘clipview’ object and any part of the clipping shape which is outside of the clipview area remains visible. Part of the confusion around the terminology is probably explained by the fact that Serif uses the same definitions as Corel uses but some people are familiar with Adobe’s reference