The issue was discovered in JDK-8316274.

javax/swing/ButtonGroup/TestButtonGroupFocusTraversal.java
the test started to fail on Ubuntu 23.10+
This was revealed due to another bug (JDK-8370624).

1. Only Motif LaF is affected.

java.awt.DefaultKeyboardFocusManager#focusNextComponent returns different components depending on the system on which it is run

Ubuntu 22.04 - the test passes, focus moves to JToggleButton
Ubuntu 23.10+ - failure, focus moves to JRadioButton

java.awt.DefaultKeyboardFocusManager#focusNextComponent call SortingFocusTraversalPolicy#getFocusTraversalCycle()
https://github.com/openjdk/jdk/blob/3e20a9392fecef796098507acef429ef2d45a3d2/src/java.desktop/share/classes/javax/swing/SortingFocusTraversalPolicy.java#L117

which uses LayoutComparator
https://github.com/openjdk/jdk/blob/3e20a9392fecef796098507acef429ef2d45a3d2/src/java.desktop/share/classes/javax/swing/LayoutComparator.java#L130-L134


The JToggleButton and JRadioButton have different component bounds on Ubuntu 22.04 and 24.04:

https://bugs.openjdk.org/secure/attachment/116610/TestButtonGroupFocusTraversal.java
a modified test that includes a copy of the LayoutComparator with debug prints.

# 22.04

Comparing javax.swing.JToggleButton to javax.swing.JRadioButton

        ax = 42, ay = 14, bx = 118, by = 5
        zOrder = -2
        Math.abs(ay - by) < ROW_TOLERANCE Math.abs(14 - 5) = 9 < 10 = true
        (ax < bx) ? -1 : ((ax > bx) ? 1 : zOrder) -1
RESULT: -1


# 24.04

Comparing javax.swing.JToggleButton to javax.swing.JRadioButton

        ax = 39, ay = 15, bx = 115, by = 5
        zOrder = -2
        Math.abs(ay - by) < ROW_TOLERANCE Math.abs(15 - 5) = 10 < 10 = false
        (ay < by) ? -1 : 1 : zOrder) 1
RESULT: 1

Note that, in the case of Ubuntu 24.04, Math.abs(ay - by) < ROW_TOLERANCE is not less that ROW_TOLERANCE, so, it's sorted differently.