diff --git a/platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java b/platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java
index 8546122d1bfa..c0ea9377f0b4 100644
--- a/platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java
+++ b/platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java
@@ -18,10 +18,7 @@ package com.intellij.codeInsight.completion;
 
 import com.intellij.codeInsight.completion.impl.CompletionServiceImpl;
 import com.intellij.codeInsight.editorActions.CompletionAutoPopupHandler;
-import com.intellij.codeInsight.lookup.LookupAdapter;
-import com.intellij.codeInsight.lookup.LookupElement;
-import com.intellij.codeInsight.lookup.LookupEvent;
-import com.intellij.codeInsight.lookup.LookupManager;
+import com.intellij.codeInsight.lookup.*;
 import com.intellij.codeInsight.lookup.impl.LookupImpl;
 import com.intellij.openapi.application.Application;
 import com.intellij.openapi.application.ApplicationManager;
@@ -91,6 +88,7 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
   private LightweightHint myHint;
   private final Semaphore myFreezeSemaphore;
   private Boolean myToRestart;
+  private boolean myRestartScheduled;
 
   private boolean myModifiersReleased;
 
@@ -273,9 +271,10 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
   }
 
   private boolean isOutdated() {
-    return myDisposed ||
-           myEditor.isDisposed() ||
-           !ApplicationManager.getApplication().isUnitTestMode() && myEditor.getComponent().getRootPane() == null;
+    if (!myDisposed) {
+      LOG.assertTrue(this == CompletionServiceImpl.getCompletionService().getCurrentCompletion());
+    }
+    return myDisposed || myEditor.isDisposed() || getProject().isDisposed();
   }
 
   private void trackModifiers() {
@@ -430,11 +429,15 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
   }
 
   public void closeAndFinish(boolean hideLookup) {
+    LOG.assertTrue(this == CompletionServiceImpl.getCompletionService().getCurrentCompletion());
+
     if (myHint != null) {
       myHint.hide();
     }
 
-    if (LookupManager.getActiveLookup(myEditor) == myLookup) {
+    Lookup lookup = LookupManager.getActiveLookup(myEditor);
+    if (lookup != null) {
+      LOG.assertTrue(lookup == myLookup);
       myLookup.removeLookupListener(myLookupListener);
       finishCompletionProcess();
 
@@ -485,15 +488,11 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
     invokeLaterIfNotDispatch(new Runnable() {
       public void run() {
         if (isOutdated()) return;
-        if (isCanceled() && myToRestart != Boolean.TRUE) return;
-
-        //what if a new completion was invoked by the user before this 'later'?
-        if (CompletionProgressIndicator.this != CompletionServiceImpl.getCompletionService().getCurrentCompletion()) return;
+        if (!isBackgrounded()) return;
+        if (isCanceled() && !myRestartScheduled) return;
 
         myLookup.setCalculating(false);
 
-        if (!isBackgrounded()) return;
-
         if (hideAutopopupIfMeaningless()) {
           return;
         }
@@ -651,17 +650,15 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
   }
 
   public void scheduleRestart() {
+    myRestartScheduled = true;
+
     if (CompletionAutoPopupHandler.ourTestingAutopopup) {
       System.out.println("CompletionProgressIndicator.scheduleRestart");
     }
 
-
     ApplicationManager.getApplication().assertIsDispatchThread();
 
-    final int offset = myEditor.getCaretModel().getOffset();
-    final long stamp = myEditor.getDocument().getModificationStamp();
     final Project project = getProject();
-    final boolean wasDumb = DumbService.getInstance(project).isDumb();
     ApplicationManager.getApplication().invokeLater(new Runnable() {
       @Override
       public void run() {
@@ -669,15 +666,7 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
           System.out.println("later");
         }
 
-        if (myEditor.isDisposed() || project.isDisposed()) {
-          return;
-        }
-
-        if (!wasDumb && DumbService.getInstance(project).isDumb()) {
-          return;
-        }
-
-        if (myEditor.getCaretModel().getOffset() != offset || myEditor.getDocument().getModificationStamp() != stamp) {
+        if (isOutdated()) {
           return;
         }
 
@@ -685,10 +674,7 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
           System.out.println("invoking");
         }
 
-
-        if (!isOutdated()) {
-          closeAndFinish(false);
-        }
+        closeAndFinish(false);
 
         final CodeCompletionHandlerBase newHandler = new CodeCompletionHandlerBase(myParameters.getCompletionType(), false, isAutopopupCompletion());
         final PsiFile psiFileInEditor = PsiUtilBase.getPsiFileInEditor(myEditor, project);
diff --git a/platform/lang-impl/src/com/intellij/codeInsight/completion/impl/CompletionServiceImpl.java b/platform/lang-impl/src/com/intellij/codeInsight/completion/impl/CompletionServiceImpl.java
index 42ef142195d2..fd8ecf13cd62 100644
--- a/platform/lang-impl/src/com/intellij/codeInsight/completion/impl/CompletionServiceImpl.java
+++ b/platform/lang-impl/src/com/intellij/codeInsight/completion/impl/CompletionServiceImpl.java
@@ -17,6 +17,7 @@ package com.intellij.codeInsight.completion.impl;
 
 import com.intellij.codeInsight.completion.*;
 import com.intellij.codeInsight.lookup.LookupElement;
+import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.editor.Document;
 import com.intellij.openapi.util.text.StringUtil;
@@ -66,6 +67,7 @@ public class CompletionServiceImpl extends CompletionService{
   }
 
   public void setCurrentCompletion(@Nullable final CompletionProgressIndicator indicator) {
+    ApplicationManager.getApplication().assertIsDispatchThread();
     if (indicator != null) {
       final CompletionProgressIndicator oldCompletion = myCurrentCompletion;
       final Throwable oldTrace = myTrace;
diff --git a/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java b/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java
index 9f6f2915e42a..e2c58419226b 100644
--- a/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java
+++ b/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java
@@ -931,7 +931,12 @@ public class LookupImpl extends LightweightHint implements Lookup, Disposable {
 
   public void restorePrefix() {
     if (myInitialPrefix != null) {
-      myEditor.getDocument().replaceString(getLookupStart(), myEditor.getCaretModel().getOffset(), myInitialPrefix);
+      performGuardedChange(new Runnable() {
+        @Override
+        public void run() {
+          myEditor.getDocument().replaceString(getLookupStart(), myEditor.getCaretModel().getOffset(), myInitialPrefix);
+        }
+      });
     }
   }
 
diff --git a/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupManagerImpl.java b/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupManagerImpl.java
index 183ec15e0819..588624db8824 100644
--- a/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupManagerImpl.java
+++ b/platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupManagerImpl.java
@@ -31,6 +31,7 @@ import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.editor.EditorFactory;
 import com.intellij.openapi.editor.event.EditorFactoryAdapter;
 import com.intellij.openapi.editor.event.EditorFactoryEvent;
+import com.intellij.openapi.project.DumbService;
 import com.intellij.openapi.project.Project;
 import com.intellij.psi.PsiDocumentManager;
 import com.intellij.psi.PsiFile;
@@ -76,6 +77,18 @@ public class LookupManagerImpl extends LookupManager {
       }
     });
 
+    bus.connect().subscribe(DumbService.DUMB_MODE, new DumbService.DumbModeListener() {
+      @Override
+      public void enteredDumbMode() {
+        hideActiveLookup();
+      }
+
+      @Override
+      public void exitDumbMode() {
+        hideActiveLookup();
+      }
+    });
+
 
     final EditorFactoryAdapter myEditorFactoryListener = new EditorFactoryAdapter() {
       public void editorReleased(EditorFactoryEvent event) {