JabRef version JabRef 3.8.1-dev--snapshot--2016-12-22--master--6f40cf8
linux 4.8.11-100.fc23.x86_64 amd64
Java 1.8.0_51 on Fedora 23

Steps to reproduce:

1. Try to fetch infos about an arXiv preprint without removing the "arXiv:" prefix, e.g. "arXiv:0710.0994"
2. A dialog appears for a second, after which nothing happens. The status line still shows "Status: Processing 0710.0994" though.
3. If one removes the prefix, i.e. enters just "0710.0994", then everything works as expected.

In the terminal I don't see any new log messages when this happens.