Ok I think I have figured this out. Even though you have defined this field as a measure, I'm guessing the source table is actually a NVARCHAR. For example I have an analytic view with an NVARCHAR(4) field for year. I decided to try to make it a measure in my semantics and see if I could add it to measures in data preview as you have done and sure enough it counts it.
The problem is that you can't sum a text field. Even though you are saying it's a measure in your definition it truly is not. I have a more recent version of Studio and I can see measure icon like in your second screenshot but it also shows an additional icon that you are not seeing in your screenshot that shows AB. See my screenshot;
