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

JabRef 5.0-dev--snapshot--2018-09-06--docbookfive--ee248ae75
Windows 7 6.1 amd64
Java 1.8.0_181

Steps to reproduce:

1. Open two libraries and the select one entry and open it with crtl-e in the entry editor
2. Put something (like a doi in my case) into the clipboard
3. Switch to the other library
4. Try to open the entry editor by double clicking one entry.

Jabref chokes and the program can only be shut down from the task manager. It only increases available RAM up to 4.4 Gb (and even further, but I did not wait for it) without doing anything. A log file or error report is not possible.