I suspect you did forget to use comet physics. Logic is, of course, vital. However, "common sense" and intuition can often lead you astray when used outside familiar subjects. I wasn't quite clear on just what you were suggesting, so if you have specific concerns or questions, could you clearly state them point by point?

A couple of general points -

(1) With extremely low gravity, little structural strength is required to retain surface features. This isn't on earth!

(2) The structure is not homogeneous. Some areas will be darker than others causing thermal variations and the material isn't just dust and ice. There are other materials, there will be gas pockets.