NX User is unable to move a Cavity Mill operation under a WORKPIECE parent object

A cavity mill operation cannot be moved under a WORKPIECE object.  NX does not let you drag and drop the operation in the Geometry view of the operation navigator. Copy and paste of the operation into the WORKPIECE will return a "data type is inconsistent" error, and the WORKPIECE object is not shown in the Geometry dropdown list within the operation.

This is because the operation already has part or blank defined in it, and you are not allowed to move the operation under a different geometry parent until you first remove the geometry in the operation.  This is not limited to cavity mill operations.  Any operation that lets the user define part or blank in it will see this same limitation.