So, this is cra cra, but we found a work around.
On the value tab, click inward rounding (your tolerances will not be right, but move on). Then on the other tab, deselect 'use dimension font' change to .75, close out the editor. click the dimension, turn off inward rounding, your tolerances will correct and the font size will remain the same.
I see that you already found a workaround but I do have another suggestion that may work for you. If all your tolerances on the drawing need to be set to 75% size of dimension you can go to "Tools>Options>Document Properties>Dimensions" then go and click on the tolerances box in the tab and set all tolerances to be 75% size. Note: This will only change newly generated dimensions and not pre-existing