When copying a part which is marked as adaptive in an assembly to a new assembly by using Windows Explorer, you cannot set the copied part as adaptive to the new assembly after inserting it. Using windows explorer the adaptively used in assembly flag will not be removed when the file is copied. To enable copied part to adapt, select Tools>Document Settings>Modeling and remove the check mark from the option. Use Save Copy As to save a copy of the open part file and the new file will have the flag cleared.