In trying to create a new KLWP I have uncovered what appears to be a known bug, but I think I can add some more clarity.
The issue appears to be that for certain Shape-type objects, when set as clipping mask, the shape is defined radiating outward from the top left corner of the bounding box. That is, the bounding box’s top-left corner defines the centre of the shape, rather than the top-left corner of the shape.
You can see a demonstration here:
The Squircle shape is affected by this issue; notice that the bounding box is in the same position in the first two images, but that the location of the shape itself when it’s set as a clipping mask versus unset is different. The Square shape is not affected and behaves as you would expect with respect to the bounding box.
This issue appears to affect the Squircle, Arc, and Path shapes. The Hexagon shape appears to have a similar issue but it’s not the same, and as I’m trying to use Paths that’s my focus, so I didn’t investigate further other than noticing it is inconsistent but apparently in a different way. Other shapes behave as expected when the boundaries are changed.
Proposal: Modify the behaviour of Squircle, Arc, and Path options to ensure that they fit within the bounding box when used as clipping masks.