Comment 3 for bug 324117

    Okay, ignore the reference to Bug 250326. The reason that the elliptical arc with non-zero rotation is causing a problem is because it is not a valid sodipodi object. You cannot create one of these using the Inkscape gui, you have to import it from an external file. If you try to create one in the gui you will get a sodipodi:type = arc for which the rotation angle by definition is zero and cannot be changed. If you rotate this object what happens is you get a rotate transform matrix but the rotation angle is still zero in the sodipodi object. So the arc with non-zero angle is not a legal (or recognized) sodipodi object, and the Simplify operation does not work.
    However, the simplify operation should still work even if the gui doesn't.
    There is also a very unfortunate side effect, which is that the operation : Path | Object to Path doesn't work either on this type of object, which is how I got onto this subject in the first place.