I noticed there are several issues with the filter effects dialog:
1. Wrong initial value for the "Type" combo box of feColorMatrix when
adding a new filter effect or loading an existing one (patch snippet
attached, please apply to 0.48 as well).
2. Undo does not work correctly: when modifying a parameter using a
slider, undo does not restore the slider to its value at the start of
the drag, but to intermediate positions during the drag. (Fixing this
likely requires a substantial rewrite.)
3. It says feComponentTransfer is not implemented in Inkscape, but in
fact it is.
4. Some sliders have completely bogus ranges. For example the surface
scale slider on feDiffuseLighting operates in the absurd range [-1000,
1000] with a step of 0.1, whereas 90% of the useful values lie in the
range [-1, 1]. [-5, 5] is a more appropriate choice. (I'll follow up
with a ptach that fixes some of the more outrageous ranges.)
Issues 2 and 3 could be worked on in the 0.49 dev cycle.