Jabref 4.0 beta 2 freeze after creating a new entry

[zhaiyusci]

JabRef version 4.0 beta 2 on Linux Mint 18.2.

After I create a new entry, the program freezes.

I also try this on JabRef 4.0.0 beta. This problem does not happen.

Steps to reproduce:

1. Open the downloaded jar file with jave -jar JabRef-4.0-beta2.jar.
2. Create a new file.
3. Create a new entry and click Article, for example.
4. The program freezes. To exit, got to terminal pressing Ctrl-C.

Sorry for the poor English.

[lenhard]

@zhaiyusci I think there is already and issue for this. It reads very much like a duplicate of #2963

Please have a look at the other issue. I'll close this one.