--- a/o.n.core/nbproject/project.xml	
+++ a/o.n.core/nbproject/project.xml	
@@ -76,7 +76,9 @@ 
                     <code-name-base>org.netbeans.swing.plaf</code-name-base>
                     <build-prerequisite/>
                     <compile-dependency/>
-                    <run-dependency/>
+                    <run-dependency>
+                        <specification-version>1.15</specification-version>
+                    </run-dependency>
                 </dependency>
                 <dependency>
                     <code-name-base>org.openide.actions</code-name-base>
--- a/o.n.core/src/org/netbeans/core/GuiRunLevel.java	
+++ a/o.n.core/src/org/netbeans/core/GuiRunLevel.java	
@@ -56,6 +56,7 @@ 
 import org.netbeans.core.startup.RunLevel;
 import org.netbeans.core.startup.Splash;
 import org.netbeans.core.startup.StartLog;
+import org.netbeans.swing.plaf.Startup;
 import org.openide.awt.StatusDisplayer;
 import org.openide.util.Lookup;
 import org.openide.util.NbBundle;
@@ -125,6 +126,8 @@ 
     /** Method to initialize the main window.
     */
     private void initializeMainWindow() {
+        Startup.setClassLoader(Lookup.getDefault().lookup(ClassLoader.class)); // #182507
+
         StartLog.logStart ("Main window initialization"); //NOI18N
 
         TimableEventQueue.initialize();
--- a/o.n.swing.plaf/manifest.mf	
+++ a/o.n.swing.plaf/manifest.mf	
@@ -1,6 +1,6 @@ 
 Manifest-Version: 1.0
 OpenIDE-Module-Localizing-Bundle: org/netbeans/swing/plaf/Bundle.properties
 OpenIDE-Module: org.netbeans.swing.plaf
-OpenIDE-Module-Specification-Version: 1.14
+OpenIDE-Module-Specification-Version: 1.15
 AutoUpdate-Show-In-Client: false
 
--- a/o.n.swing.plaf/src/org/netbeans/swing/plaf/Startup.java	
+++ a/o.n.swing.plaf/src/org/netbeans/swing/plaf/Startup.java	
@@ -318,11 +318,21 @@ 
         
     }
 
+    private static ClassLoader loader;
+    /**
+     * Set a class loader to be used in place of {@link Thread#getContextClassLoader}.
+     * @param loader a system-wide class loader
+     * @since org.netbeans.swing.plaf 1.15
+     */
+    public static void setClassLoader(ClassLoader loader) {
+        Startup.loader = loader;
+    }
+
     /** Gets the value of system class loader and returns it.
      */
     private static final class CLValue implements UIDefaults.ActiveValue {
-        public Object createValue (UIDefaults defs) {
-            return Thread.currentThread().getContextClassLoader();
+        public @Override ClassLoader createValue(UIDefaults defs) {
+            return loader != null ? loader : Thread.currentThread().getContextClassLoader();
         }
     }