There have been many issues with objects. From my experience, this one can be solved by simply deleting the shaders attached to the object in reverse order. For example, if I have an object named Object, and Object has a multi shader, and that multi shader has an image map shader, first delete the image map shader, then the multishader, and then Object. From my experience, this should fix it.
As for undos, that's definitely something Planetside has in mind, although it will probably be pretty tough to implement.