Possible to post a screenshot of the dimension before and during edit?
I was going to ask about your default units or if they were showing Metric vs. English but these should not change when you simply edit the dimension. Nor should the Diameter vs. Radius pose a problem as that would be self explanatory.
Seems like I remember (which is happening less often every day....) having that issue once. The problem had something to do with the Dimension Type had been inadvertently set to "True" vs "Projected", or some such....