If I have a circle and its diameter is dimensioned with a parameter. Then I toggle that dimension from Diameter to Radius, The circle will display a radius type dimension, but it will no longer be bound to a parameter. I suggest when toggling a dimension from diameter to radius that it be bound to the original parameter divided by 2. For example if the parameter for the diameter was X, then after toggling the dimension from diameter to radius the dimension would be bound to X/2.