Thanks very much for finding a workaround, I spent a day or so on this and didn't think to group the mask elements. I still think it is a bug in the Inkscape renderer though. The 'mask' element is itself a grouping element according to the spec, so I do think what I had done here should work.
Thanks very much for finding a workaround, I spent a day or so on this and didn't think to group the mask elements. I still think it is a bug in the Inkscape renderer though. The 'mask' element is itself a grouping element according to the spec, so I do think what I had done here should work.
But at this stage this is an easy work around.