Comment 11 for bug 404009

With regard to the ChALKeR's example: AFAICT the difference is how the initial size (width / height of the <svg> element) affects the size of the mask (it gets clipped to the size of the <svg> + 10%), whereas Inkscape does not clip the mask at all, even if it (partially) is outside the defined initial viewport.

Tests can be done by increasing/decreasing the 'width' attribute if the <svg> element by 100px steps: the the left edge of the visible portion of the masked rectangle will shift by 10 px (direction depending on whether the width was increased or decreased).