diff --git a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/FoldingTest.java b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/FoldingTest.java
index cee355b87f1..73154175c44 100644
--- a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/FoldingTest.java
+++ b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/FoldingTest.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2006 Wind River Systems, Inc. and others.
+ * Copyright (c) 2006, 2007 Wind River Systems, Inc. and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -141,7 +141,7 @@ public class FoldingTest extends TestCase {
 		return (Position[]) positions.toArray(new Position[positions.size()]);
 	}
 
-	public void testFoldingPositions() throws BadLocationException {
+	public void testInitialFolding() throws BadLocationException {
 		Position[] actual= getFoldingPositions();
 		Position[] expected= new Position[] {
 				createPosition(0, 2),
@@ -170,4 +170,26 @@ public class FoldingTest extends TestCase {
 		assertEqualPositions(expected, actual);
 	}
 	
+	public void testToggleFolding_Bug186729() throws BadLocationException {
+		fEditor.getAction("FoldingToggle").run();
+		IPreferenceStore store= CUIPlugin.getDefault().getPreferenceStore();
+		store.setValue(PreferenceConstants.EDITOR_FOLDING_PREPROCESSOR_BRANCHES_ENABLED, false);
+		fEditor.getAction("FoldingToggle").run();
+		
+		Position[] actual= getFoldingPositions();
+		Position[] expected= new Position[] {
+				createPosition(0, 2),
+				createPosition(4, 7),
+				createPosition(29, 31),
+				createPosition(35, 40),
+				createPosition(42, 46),
+				createPosition(48, 55),
+				createPosition(51, 53),
+				createPosition(57, 59),
+				createPosition(61, 63),
+				createPosition(65, 67),
+		};
+		if (false) System.out.println(toString(actual));
+		assertEqualPositions(expected, actual);
+	}
 }
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/actions/FoldingActionGroup.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/actions/FoldingActionGroup.java
index 019644b0ec7..adb31073c9c 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/actions/FoldingActionGroup.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/actions/FoldingActionGroup.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2006 IBM Corporation and others.
+ * Copyright (c) 2000, 2007 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -38,6 +38,7 @@ public class FoldingActionGroup extends ActionGroup {
 	private static abstract class PreferenceAction extends ResourceAction implements IUpdate {
 		PreferenceAction(ResourceBundle bundle, String prefix, int style) {
 			super(bundle, prefix, style);
+			update();
 		}
 	}
 	
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/editor/CEditor.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/editor/CEditor.java
index cac83bbfcb2..037ffceb2db 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/editor/CEditor.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/editor/CEditor.java
@@ -1097,6 +1097,12 @@ public class CEditor extends TextEditor implements ISelectionChangedListener, IC
 	 */
 	private ListenerList fReconcilingListeners= new ListenerList(ListenerList.IDENTITY);
 
+	/**
+	 * Flag indicating whether the reconciler is currently running.
+	 * @since 4.0
+	 */
+	private volatile boolean fIsReconciling;
+
 	/**
 	 * Semantic highlighting manager
 	 * @since 4.0
@@ -1526,7 +1532,7 @@ public class CEditor extends TextEditor implements ISelectionChangedListener, IC
 	 * @since 4.0
 	 */
 	protected void synchronizeOutlinePage() {
-		if(fOutlinePage != null && fOutlinePage.isLinkingEnabled()) {
+		if(fOutlinePage != null && fOutlinePage.isLinkingEnabled() && !fIsReconciling) {
 			fOutlinePage.removeSelectionChangedListener(this);
 			fOutlinePage.synchronizeSelectionWithEditor();
 			fOutlinePage.addSelectionChangedListener(this);
@@ -2510,7 +2516,8 @@ public class CEditor extends TextEditor implements ISelectionChangedListener, IC
 	 * @since 4.0
 	 */
 	public void aboutToBeReconciled() {
-
+		fIsReconciling= true;
+		
 		// Notify AST provider
 		CUIPlugin.getDefault().getASTProvider().aboutToBeReconciled(getInputCElement());
 
@@ -2526,7 +2533,8 @@ public class CEditor extends TextEditor implements ISelectionChangedListener, IC
 	 * @since 4.0
 	 */
 	public void reconciled(IASTTranslationUnit ast, IPositionConverter positionTracker, IProgressMonitor progressMonitor) {
-
+		fIsReconciling= false;
+		
 		CUIPlugin cuiPlugin= CUIPlugin.getDefault();
 		if (cuiPlugin == null)
 			return;
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/folding/DefaultCFoldingStructureProvider.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/folding/DefaultCFoldingStructureProvider.java
index ff5f03877ec..ee8cdf33230 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/folding/DefaultCFoldingStructureProvider.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/folding/DefaultCFoldingStructureProvider.java
@@ -112,10 +112,8 @@ public class DefaultCFoldingStructureProvider implements ICFoldingStructureProvi
 			try {
 				FoldingStructureComputationContext ctx= createContext(fInitialReconcilePending);
 				fInitialReconcilePending= false;
-				if (fPreprocessorBranchFoldingEnabled) {
-					ctx.fAST= ast;
-					ctx.fASTPositionConverter= positionTracker;
-				}
+				ctx.fAST= ast;
+				ctx.fASTPositionConverter= positionTracker;
 	            update(ctx);
 			} finally {
 				fReconciling= false;
@@ -1067,7 +1065,7 @@ public class DefaultCFoldingStructureProvider implements ICFoldingStructureProvi
 				computeFoldingStructure(ast, ctx);
 			}
 		}
-		if (!fInitialReconcilePending) {
+		if (!fInitialReconcilePending || isConsistent(fInput)) {
 			IParent parent= (IParent) fInput;
 			try {
 				computeFoldingStructure(parent.getChildren(), ctx);
@@ -1075,7 +1073,17 @@ public class DefaultCFoldingStructureProvider implements ICFoldingStructureProvi
 			}
 		}
 	}
-
+	
+	static boolean isConsistent(ICElement element) {
+		if (element instanceof ITranslationUnit) {
+			try {
+				return ((ITranslationUnit)element).isConsistent();
+			} catch (CModelException exc) {
+			}
+		}
+		return false;
+	}
+	
 	/**
 	 * Compute folding structure of the preprocessor branches for the given AST.
 	 *