Automatic creation of enable-background attribute not undone in renderer

1. Open a document, any document.
2. Create a filter with a filter primitive operating on "Background Image" and apply it to an object. As documented (whether expected or not) this won't work as the enable-background attribute/style value has not been set yet. (It'd be good if using it like this would automatically turn it on, but that's a feature request, not a bug fix).
3. Go to the layer selection panel, select a layer blending mode. The filter in the previous step should now start to function correctly as enable-background is set to "new".
4. Undo. This removes the filter on the layer and also removes the enable-background setting in the document (observe by saving or the XML editor).
5. Observe that the enable-background setting has been disabled (save or look in the XML editor). This is as expected as it was created by the action.
6. Observe however that filters using the "Background Image" are still working in the renderer, until you reopen or revert the document (to after the undo state). This should not be. The rendering canvas is not being told that enable-background has been removed.

Ubuntu 10.04, Inkscape-0.47+devel-r9474