JabRef version

JabRef 5.1--2020-03-23--67daf36
Linux 5.4.0-4-amd64 amd64 
Java 14

Debian bullseye/sid with i3 window manager.

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

Before, the groups panel would stay at it's size when the window is resized.
Now, it seems to scale proportionally with the whole window.
This is especially annoying when a tiling window manager is used and you open a PDF next to jabref: in this case the groups panel scales to about 50% of the whole window.

Steps to reproduce the behavior:

1. resize jabref window
2. groups panel scales proportionally instead of keep size