A problem has come up and it's very interesting...editing witness lines and the dimension text moving if an existing dimension text has been moved from it's "home" location. It even looks like the added dimension text isn't placed in the correct location.
Take a look at the video below to see what happens.
So, for the time being...don't edit witness lines if you've moved any text in your dimensions and want to add to it. Just create a new dimension string.
I submitted this to Autodesk and it's currently being investigated by the development team...seems like the story of all the issues I run into!