I don't really know if its a bug or a feature:
If I set an inset for a clippingpath (made in Photoshop) by for example 3mm, it sets the inset based on the scaling of the image. Means: if my image is scaled by 50% the inset will only be 1,5mm. As I have a document with multiple scale ratios it is not possible to maintain a coherent inset amount.
I use the clipping-path frame to generate a cutting contours for stickers which all have to have a specific inset to avoid "blank streaks".