JabRef 4.0-dev--snapshot--2017-08-31--master--54e0994ba
Windows 10 10.0 amd64
Java 1.8.0_141

This isn't really a bug, it's more an observation I made that I wanted to share, as it might affect some users.

Steps to reproduce:

1. Open an item in the entry editor
2. Keep the entry editor open and select another item
3. The new item is opened in the entry editor
4. Do this multiple times
5. The Windows Task Manager shows a massive increase in the used CPU power (up to 95% on a Corei7 4+4HT system)
6. Indeed, the responsiveness of the entry editor does not feel as quick as with 3.8.2 - it is still ok on my machine, I guess, but people with a slower CPU might experience bigger performance issues

Note, that this might be also related to the size of the databse (>6k entries).
Note furthermore, that this issue does not appear, if the entry editor is closed.