If the points of a dimension were snapped to points of objects when they were created, or when a segment was selected, the dimension stays associated with the object points. If the object point is subsequently moved through a modeling operation, such as the Reshape tool, the dimension is automatically adjusted to follow the moved point. There are a number of modeling operations, which will not be able to maintain the associativity of a dimension with its referenced object. If this occurs, and the object is moved, the dimension will not follow along. However, this condition can easily be fixed with the following steps:


Select the dimension with the pick tool and turn on its controls (hit the f6 key or press the Show Controls button in the Tool Options palette).


Make sure that object snapping is enabled.


Select each dimension point control and move it back on the desired object point, using snapping. Sometimes this may mean snapping it back to the same point it already appeared on. The snapping will recreate the associativity.


Now, if the referenced object points are moved, the dimension will follow along.