Test javax/swing/JInternalFrame/8020708/bug8020708.java fails on Ubuntu

Testsuite name: jdk_swing
Test name(s):javax/swing/JInternalFrame/8020708/bug8020708.java
Product(s) tested: JDK 11.0.4b07
OS/architecture: Ubuntu 19.04

Reproducible: Always
Reproducible on machine: llg00tuo.uk.oracle.com (Ubuntu 19.04)

Is it a Regression: No, Fails for Previous GA Release JDK11.0.3b11

Does it affect JDK13 : Yes, Fails with JDK13b24

Is it a platform specific issue: Yes. Specific to Ubuntu19.04
Ubuntu19.04 : Fail ( llg00tuo.uk.oracle.com)
Ubuntu18.04 : Pass(llg00tug.uk.oracle.com)
Oracle Linux : Pass (llg00fza.uk.oracle.com)

Exception/Error from log:
Caused by: java.lang.RuntimeException: Close mnemonic does not work in [The CDE/Motif Look and Feel - com.sun.java.swing.plaf.motif.MotifLookAndFeel]