I had an Assembly where I created a New part within the Assembly, and even edited the part to some extent. Then I closed the Assembly window and further edited the part in a normal Part editing window. When I went back to the Assembly, the edited part wouldn't always behave like I wanted it to (like re-orienting it did not behave normally). The HINT IS THIS: If you have created a new part within an Assembly, but then you edit it outside the Assembly window, the best thing to do is delete the part from the Assembly and then re-insert it. Otherwise, there are constraints left over from the original creation of the part that may prevent you from doing what you want to do.