The logic in drawTiledShadow does not work together with the new filter effect absolute paint rect. On FEGaussianBlur we determine the inflation rect and cairo is doing it as well.
Hopefully this shouldn't be an issue for too much longer, if https://bugs.webkit.org/show_bug.cgi?id=46475 lands.
drawTiledShadow is now part of ContextShadow, so this issue can be closed.