diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1af0b76..e10fd43 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+- Fixed a "Warning" dialog showing raw XML content sometimes appearing at IDE startup after using a diff view
+
 # 1.2.25 (2026-06-29)
 
 - Fixed choice menu not appearing when option descriptions span more than 3 terminal lines
diff --git a/pom.xml b/pom.xml
index 4dbf77a..10714a4 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,7 +6,7 @@
 
     <groupId>io.github.nbplugins</groupId>
     <artifactId>netbeans-plugin-claude-code-gui</artifactId>
-    <version>1.2.25-SNAPSHOT</version>
+    <version>1.2.27-SNAPSHOT</version>
     <packaging>nbm</packaging>
     <name>Netbeans Plugin Claude Code GUI</name>
     <description>NetBeans plugin that provides a GUI for Claude Code CLI — run claude code sessions directly inside the IDE.</description>
diff --git a/src/main/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiff.java b/src/main/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiff.java
index f7f9de5..fea7461 100644
--- a/src/main/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiff.java
+++ b/src/main/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiff.java
@@ -221,13 +221,7 @@ public Writer createWriter(Difference[] conflicts) throws IOException {
                         // Override componentClosed() so that closing the tab without clicking
                         // Approve or Reject sends FILE_REJECTED — preventing Claude from hanging.
                         final String finalDiffTabName = diffTabName;
-                        TopComponent diffTC = new TopComponent() {
-                            @Override
-                            public void componentClosed() {
-                                super.componentClosed();
-                                DiffTabTracker.setRejected(finalDiffTabName);
-                            }
-                        };
+                        TopComponent diffTC = new DiffTopComponent(finalDiffTabName);
                         diffTC.setDisplayName(diffTabName);
                         diffTC.setLayout(new java.awt.BorderLayout());
 
@@ -305,4 +299,28 @@ public void setHandler(AsyncHandler<OpenDiffResult> handler) {
             return createAsyncResponse(createErrorResult("Error opening diff: " + e.getMessage()));
         }
     }
+
+    /**
+     * Ephemeral diff-viewer tab. Must never be persisted across IDE restarts — its toolbar
+     * button listeners close over per-request state (file contents, async response handler)
+     * that is not meaningfully serializable.
+     */
+    static final class DiffTopComponent extends TopComponent {
+        private final String diffTabName;
+
+        DiffTopComponent(String diffTabName) {
+            this.diffTabName = diffTabName;
+        }
+
+        @Override
+        public int getPersistenceType() {
+            return TopComponent.PERSISTENCE_NEVER;
+        }
+
+        @Override
+        public void componentClosed() {
+            super.componentClosed();
+            DiffTabTracker.setRejected(diffTabName);
+        }
+    }
 }
diff --git a/src/test/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiffTest.java b/src/test/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiffTest.java
new file mode 100644
index 0000000..aa3ff34
--- /dev/null
+++ b/src/test/java/io/github/nbplugins/claudecodegui/mcp/tools/OpenDiffTest.java
@@ -0,0 +1,22 @@
+package io.github.nbplugins.claudecodegui.mcp.tools;
+
+import org.junit.jupiter.api.Test;
+import org.openide.windows.TopComponent;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Unit tests for {@link OpenDiff}.
+ */
+class OpenDiffTest {
+
+    @Test
+    void diffTopComponentPersistenceTypeIsNever() {
+        // Reproduces the bug where the diff tab's TopComponent defaulted to PERSISTENCE_ALWAYS,
+        // causing the NetBeans window system to try to serialize it (and the non-serializable
+        // async-handler state it closes over) into a .settings file on IDE exit — producing a
+        // corrupted-settings "Warning" dialog with raw XML on the next startup.
+        OpenDiff.DiffTopComponent tc = new OpenDiff.DiffTopComponent("Diff: test");
+        assertEquals(TopComponent.PERSISTENCE_NEVER, tc.getPersistenceType());
+    }
+}