I spend quite a a bit of time looking at the PDF in question. The image is a Jpeg that doesn't appear to have any transparency encoded in it. Pretty sure that becuase this image is being painted in a transparency group that it's the group that is responsible for making the images background transparent.

If offer some support for transparency groups but this level of support has yet to be obtained.

days light saving, little foggy this morning,

The PDF in question has a watch image that is obscuring text, the image/document contains transparency groups but I can't find anything specific that would indicate the application of alpha or an image mask. There is also some image metadata that I've yet to interpret, might be something there.

A lot of work has gone into improving our support for transparency groups particularly around various blending modes. As result this PDF is now correctly rendering using a multiply blend mode.

Marking a fixed.