In entry types editor selected field is not removed after first click

[dawidm]

JabRef 5.2--2020-09-22--129c36e
Ubuntu 20.04 (Linux 5.4.0-42-generic amd64)
Java 15

• Mandatory: I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists

When a field is selected, it's not removed after the first click on it's remove icon. Doesn't happen for the fields that are not selected.

Steps to reproduce the behavior:

1. Open entry types editor
2. Select one of available entry type fields
3. Click on remove icon for it - the field is not removed
4. Click on the icon again - the field is removed