The test javax/swing/JRootPane/DefaultButtonTest.java intermittently fails on Ubuntu 20.04 22.04 with the following diagnostic:

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#section:main
----------messages:(7/275)----------
command: main DefaultButtonTest
reason: User specified action: run main DefaultButtonTest
started: Sun Apr 09 01:55:32 CEST 2023
Mode: othervm
Additional options from @modules: --add-modules java.desktop
finished: Sun Apr 09 01:55:32 CEST 2023
elapsed time (seconds): 0.759
----------configuration:(3/40)----------
Boot Layer
  add modules: java.desktop

----------System.out:(3/169)----------
Testing L&F: javax.swing.plaf.metal.MetalLookAndFeel
Test Passed for L&F: javax.swing.plaf.metal.MetalLookAndFeel
Testing L&F: javax.swing.plaf.nimbus.NimbusLookAndFeel
----------System.err:(12/892)----------
java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.nimbus.NimbusLookAndFeel
at DefaultButtonTest.runTest(DefaultButtonTest.java:110)
at DefaultButtonTest.main(DefaultButtonTest.java:47)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:578)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:125)
at java.base/java.lang.Thread.run(Thread.java:1630)

JavaTest Message: Test threw exception: java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.nimbus.NimbusLookAndFeel
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.nimbus.NimbusLookAndFeel
====================8<--------------------

The issue was observed with 21-ea+17-1421

As for 20+36-2344 the test fails for javax.swing.plaf.metal.MetalLookAndFeel

====================8<--------------------
----------System.out:(1/53)----------
Testing L&F: javax.swing.plaf.metal.MetalLookAndFeel
----------System.err:(12/886)----------
java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.metal.MetalLookAndFeel
at DefaultButtonTest.runTest(DefaultButtonTest.java:110)
at DefaultButtonTest.main(DefaultButtonTest.java:47)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:578)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:125)
at java.base/java.lang.Thread.run(Thread.java:1623)

JavaTest Message: Test threw exception: java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.metal.MetalLookAndFeel
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.RuntimeException: Test Failed, Default Button not pressed for L&F: javax.swing.plaf.metal.MetalLookAndFeel
====================8<--------------------

Reproducibility: ~70%

Steps to reproduce:

$ runme.sh jtreg [test_jdk] "" test/jdk/javax/swing/JRootPane/DefaultButtonTest.java

see the attached runme.sh

Please note: the issue is also reproducible on Windows 10, Windows 11