Its the DIMASO system variable (or DIMASSOC for 200+).
DIMASO DDIM
Type: Switch
Saved in: Drawing
Initial value: On
Controls the associativity of dimension objects.
Off Creates no association between the various elements of the dimension. The lines, arcs, arrowheads, and text of a dimension are drawn as separate objects.
On Creates an association between the elements of the dimension. The elements are formed into a single object. If the definition point on the object moves, the dimension value is updated.