Well, it looks like Inkscape's behavior is non-compliant at the moment, but only under certain combinations of transformations (generally, rotation + non-uniform scaling). bulia and I have been discussing this, and since reworking filters will take a while, we think we have two options for this release:
1. leave the behavior as it is
2. disable filter rendering when the output would be non-compliant
#1 has the advantage that the bug would be less noticeable (fewer user complaints until the next release when it's fixed), and it has the disadvantage that the bug would be less noticeable (people getting bitten when the rendering behavior changes in the next release).
#2 has the advantage that it actively discourages people from using filters in situations where Inkscape can't currently render them properly. It has the disadvantage that it might actively discourage them from using filters.
Which one should we go with? Other suggestions?
-mental