you need to toggle that dimension to a driving (red) dimension.
Select the little lock icon to the right of the dimension input box.
Unlocked = Driven dimension (reference dim)
Locked = driving dims
I knew it was one of those setting but i tunred off automatic update on my machine and tested and it still worked so i knew i was wrong and was waitign for one of you all to jump in ,,... thx for the reminder.