CLIENT - unhandled error in GUI - IllegalStateException

Error type: CLIENT - unhandled error in GUI - IllegalStateException

Client version: 1.4.58-V1 (build: 2025-10-06 20:20)
Java version: 1.8.0_201
Default charset: UTF-8

mage.client.components.ColorPane[,0,0,0x0,invalid,layout=java.awt.BorderLayout,alignmentX=0.0,alignmentY=0.0,border=javax.swing.border.EmptyBorder@5d902e52,flags=16777504,maximumSize=,minimumSize=,preferredSize=,caretColor=,disabledTextColor=DerivedColor(color=142,143,145 parent=nimbusDisabledText offsets=0.0,0.0,0.0,0 pColor=142,143,145,editable=false,margin=javax.swing.plaf.InsetsUIResource[top=0,left=0,bottom=0,right=0],selectedTextColor=DerivedColor(color=255,255,255 parent=nimbusSelectedText offsets=0.0,0.0,0.0,0 pColor=255,255,255,selectionColor=DerivedColor(color=57,105,138 parent=nimbusSelectionBackground offsets=0.0,0.0,0.0,0 pColor=57,105,138,kit=javax.swing.text.html.HTMLEditorKit@18729393,typeHandlers=] is not attached to a horizontal group

Stack trace:
org.jdesktop.layout.GroupLayout.checkComponents(GroupLayout.java:986)
org.jdesktop.layout.GroupLayout.prepare(GroupLayout.java:940)
org.jdesktop.layout.GroupLayout.layoutContainer(GroupLayout.java:806)
java.awt.Container.layout(Container.java:1513)
java.awt.Container.doLayout(Container.java:1502)
java.awt.Container.validateTree(Container.java:1698)
java.awt.Container.validateTree(Container.java:1707)
java.awt.Container.validateTree(Container.java:1707)
java.awt.Container.validateTree(Container.java:1707)
java.awt.Container.validateTree(Container.java:1707)
and other 22 lines

Start with mage.client.components.ColorPane and trace how it is added to the GUI layout; the stack trace points to org.jdesktop.layout.GroupLayout.checkComponents. Reproduce the error in client version 1.4.58-V1 and identify the layout configuration that leaves ColorPane unattached to a horizontal group; done means the GUI lays out without this IllegalStateException.

Written by the indexing model from the issue text.