OS: Xubuntu 17.04
Computer keyboard map: Brazilian ABNT2
Java version:
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-0ubuntu1.17.04.1-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)

JabRef version: JabRef-4.0-dev--snapshot--2017-07-19--master--2f12fecfb.jar

I can't insert (only) these accentuated character (comma separated) : ~, ^, `, ', "
Because of this, I can't make these letters: à, á, ã, â, ô, ó, ò, é, ê, ü, etc.
I can't insert these on Fields or Biblatex source tabs;
(Edit to reduce ambiguity) Inserting others special characters works ok: $, %, &, *, (, º