diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/AbstractCompareViewerInformationControl.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/AbstractCompareViewerInformationControl.java
index 80721b725ad..df67cc2f7c8 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/AbstractCompareViewerInformationControl.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/AbstractCompareViewerInformationControl.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2007, 2011 Wind River Systems, Inc. and others.
+ * Copyright (c) 2007, 2012 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
@@ -233,6 +233,14 @@ public abstract class AbstractCompareViewerInformationControl extends org.eclips
 		}
 	}
 
+	@Override
+	public void setVisible(boolean visible) {
+		super.setVisible(visible);
+		if (!visible) {
+			setInput(null);
+		}
+	}
+
 	@Override
 	public void dispose() {
 		if (!fIsSystemBackgroundColor) {
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroCompareViewer.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroCompareViewer.java
index 0122af6f4cd..d392356e60a 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroCompareViewer.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroCompareViewer.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2008, 2009 Wind River Systems, Inc. and others.
+ * Copyright (c) 2008, 2012 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
@@ -199,20 +199,21 @@ class CMacroCompareViewer extends CMergeViewer {
 			fLeftViewer.setRedraw(false);
 			fRightViewer.setRedraw(false);
 		}
-		final ReplaceEdit[] edits;
+		ReplaceEdit[] edits = null;
 		
 		try {
-			final IMacroExpansionStep step;
-			if (fStepIndex < fInput.fExplorer.getExpansionStepCount()) {
-				step= fInput.fExplorer.getExpansionStep(fStepIndex);
-			} else {
-				step= fInput.fExplorer.getFullExpansion();
-			}
-			edits= step.getReplacements();
-
-			fLeftHighlighter.setReplaceEdits(fPrefixLength, edits);
-			fRightHighlighter.setReplaceEdits(fPrefixLength, edits);
+			if (fInput != null) {
+				final IMacroExpansionStep step;
+				if (fStepIndex < fInput.fExplorer.getExpansionStepCount()) {
+					step= fInput.fExplorer.getExpansionStep(fStepIndex);
+				} else {
+					step= fInput.fExplorer.getFullExpansion();
+				}
+				edits= step.getReplacements();
 	
+				fLeftHighlighter.setReplaceEdits(fPrefixLength, edits);
+				fRightHighlighter.setReplaceEdits(fPrefixLength, edits);
+			}	
 			super.setInput(input);
 			
 		} finally {
@@ -221,7 +222,7 @@ class CMacroCompareViewer extends CMergeViewer {
 				fRightViewer.setRedraw(true);
 			}
 		}
-		if (edits.length > 0) {
+		if (edits != null && edits.length > 0) {
 			if (fLeftViewer != null && fRightViewer != null) {
 				final int firstDiffOffset= fPrefixLength + edits[0].getOffset();
 				fLeftViewer.revealRange(firstDiffOffset, edits[0].getLength());
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionControl.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionControl.java
index 10b2d813551..2ee273679d5 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionControl.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionControl.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2007, 2009 Wind River Systems, Inc. and others.
+ * Copyright (c) 2007, 2012 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
@@ -64,10 +64,19 @@ public class CMacroExpansionControl extends AbstractSourceViewerInformationContr
 			fInput= macroExpansionInput;
 			updateStatusText();
 		} else {
+			fInput = null;
 			super.setInput(input);
 		}
 	}
 
+	@Override
+	public void setVisible(boolean visible) {
+		super.setVisible(visible);
+		if (!visible) {
+			setInput(null);
+		}
+	}
+
 	private void updateStatusText() {
 		if (fInput == null) {
 			return;
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionExplorationControl.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionExplorationControl.java
index 9b0ee8018c4..888bd2050a5 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionExplorationControl.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/c/hover/CMacroExpansionExplorationControl.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2007, 2010 Wind River Systems, Inc. and others.
+ * Copyright (c) 2007, 2012 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
@@ -450,11 +450,14 @@ public class CMacroExpansionExplorationControl extends AbstractCompareViewerInfo
 	public void setInput(Object input) {
 		if (input instanceof CMacroExpansionInput) {
 			setMacroExpansionInput((CMacroExpansionInput) input);
-		} else {
+		} else if (input != null) {
 			if (fMacroCompareViewer != null) {
 				fMacroCompareViewer.setMacroExpansionStep(fIndex);
 			}
 			super.setInput(input);
+		} else {
+			setMacroExpansionInput(null);
+			super.setInput(input);
 		}
 	}
 
@@ -507,6 +510,9 @@ public class CMacroExpansionExplorationControl extends AbstractCompareViewerInfo
 	 */
 	private void setMacroExpansionInput(CMacroExpansionInput input) {
 		fInput= input;
+		if (fMacroCompareViewer != null) {
+			fMacroCompareViewer.setMacroExpansionInput(input);
+		}
 		if (fInput != null) {
 			fIndex= fixIndex(input.fStartWithFullExpansion ? getStepCount() : 0);
 			showExpansion();