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

JabRef 5.0-dev--snapshot--2018-07-02--master--aed7712bc
Windows 7 6.1 amd64
Java 1.8.0_172

Steps to reproduce:

1. open the dialogue by Ctrl-N
2. Try to add a DOI identity
3. Press "erzeugen"
   and wait for an indeterminate amount of time

If you waited for several minutes the dialogue cannot be finished either by clicking "Abbrechen" not by clicking the "x" in the title line. Program had to be canceled.

I am not able by Copy and Paste the DOI content of an entry into the "Neuer Eintrag" dialogue!!