Comment 3 for bug 1004887

Attaching reduced test case (based on the provided original PDF file): the nested structure resulting from the PDF import is flattened step by step, to narrow down the cause. The minimal structure triggering the issue (missing or displaced mask?) looks like this:

1) Mask information (in <defs>):
<mask
       maskUnits="userSpaceOnUse"
       x="0"
       y="0"
       width="1"
       height="1"
       id="mask162"><image
         width="1"
         height="1"
         xlink:href="data:image/png; (…)"
         id="image164" />
</mask>

2) Masked bitmap image (width = height = 1) inside scaled group:
<g
       transform="matrix(8.429732,0,0,8.429732,353.08084,382.57798)"
       id="g4641"><image
         id="image4643"
         mask="url(#mask162)"
         xlink:href="data:image/png; (…)"
         transform="matrix(1,0,0,-1,0,1)"
         height="1"
         width="1" />
</g>