JabRef version
JabRef 4.0.0-dev--snapshot--2017-05-31--master--c9566c2a9
Linux 4.10.0-21-generic amd64
Java 1.8.0_131

Steps to reproduce:

1. I edit a field, e.g., shorthand (which I've added to the "Required Fields" tab)
2. I go to the "{} biblatex source" tab and edit the shorthand field
3. Returning to the "Required Fields" tab, the shorthand field is not updated.