Field Type: Read Only + Fetch From

What shoulld be the behaviour of the Read Only field types with a fetch from?

If I look at the filed mobile_no in Customer Doctype of Erp Next. This is a Read Only and it is fetched from the contact .

After update the mobile number in the Contact doctype the Mobile field is not update. So it seem that once it is set you cannot change. Intuitively I would expect the fetch from to update the field.

I tried the is virtual option but it does not change the behaviour

Is this a bug?

I think it’s not updated instantly. Clear the Customer’s Primary Contact and again select that contact. It will be updated.

Hi, yes I see that works but it seem a very odd step to perform. Is there any way to have these fields to be automatically update or have some kind of jobs that every day for example reupdates all fetched fields?