The document http://phroy.lost-oasis.net/ll/sumatrapdf/tableur-exo.pdf used to render correctly, but no longer does since the major refactoring in March(?) 2009.
Our interpolation of images on the edge is wrong. We interpolate the edges as if the outside of the image was transparent instead of clamping to the edge colors. We're also off by half a texel since the interpolation only occurs towards one side in these examples where the images are 1x1 in size. The bug was not as apparent before the patch that removed an "optimization" where these 1x1 images were replaced by solid rectangle fills. That optimization didn't work for 1x1 images with transparency.
Added two patches to the darcs repository that should fix all image interpolation and image pixel offset bugs similar to this one.