JabRef 5.0-beta.409--2020-02-09--6a9c915
Windows 10 10.0 amd64
Java 13.0.2

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

Steps to reproduce the behavior:

1. Open the file in the new JabRef5
2. Open the file in the old JabRef4.3
3. See screenshot below

Guys, backwards compatibility with Bibtex/Biblatex is quite important, especially if one is working across OSes and has a bibliography carefully tweaked and collected for decades!