Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1162001)
+++ lucene/CHANGES.txt	(working copy)
@@ -50,7 +50,10 @@
   throw NoSuchDirectoryException when all files written so far have been
   written to one directory, but the other still has not yet been created on the
   filesystem.  (Robert Muir)
-  
+
+* LUCENE-3402: term vectors disappeared from the index if optimize() was called
+  following addIndexes(). (Shai Erera)
+     
 New Features
 
 * LUCENE-3290: Added FieldInvertState.numUniqueTerms 
Index: lucene/src/test/org/apache/lucene/search/TestTermVectors.java
===================================================================
--- lucene/src/test/org/apache/lucene/search/TestTermVectors.java	(revision 1162001)
+++ lucene/src/test/org/apache/lucene/search/TestTermVectors.java	(working copy)
@@ -17,11 +17,15 @@
  * limitations under the License.
  */
 
+import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.analysis.MockTokenizer;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
+import org.apache.lucene.document.Field.Index;
+import org.apache.lucene.document.Field.Store;
+import org.apache.lucene.document.Field.TermVector;
 import org.apache.lucene.index.*;
 import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.store.Directory;
@@ -443,4 +447,84 @@
     }
     reader.close();
   }
+
+  private IndexWriter createWriter(Directory dir) throws IOException {
+    return new IndexWriter(dir, newIndexWriterConfig(TEST_VERSION_CURRENT,
+        new MockAnalyzer(random)));
+  }
+
+  private void createDir(Directory dir) throws IOException {
+    IndexWriter writer = createWriter(dir);
+    writer.addDocument(createDoc());
+    writer.close();
+  }
+
+  private Document createDoc() {
+    Document doc = new Document();
+    doc.add(new Field("c", "aaa", Store.YES, Index.ANALYZED, TermVector.WITH_POSITIONS_OFFSETS));
+    return doc;
+  }
+
+  private void verifyIndex(Directory dir) throws IOException {
+    IndexReader r = IndexReader.open(dir);
+    int numDocs = r.numDocs();
+    for (int i = 0; i < numDocs; i++) {
+      TermFreqVector tfv = r.getTermFreqVector(i, "c");
+      assertNotNull("term vectors should not have been null for document " + i, tfv);
+    }
+    r.close();
+  }
+  
+  public void testOptimizeAddDocs() throws Exception {
+    Directory target = newDirectory();
+    IndexWriter writer = createWriter(target);
+    for (int i = 0; i < 2; i++) {
+      writer.addDocument(createDoc());
+      writer.commit();
+    }
+    writer.optimize();
+    writer.close();
+    
+    verifyIndex(target);
+    target.close();
+  }
+
+  public void testOptimizeAddIndexesDir() throws Exception {
+    Directory[] input = new Directory[] { newDirectory(), newDirectory() };
+    Directory target = newDirectory();
+    
+    for (Directory dir : input) {
+      createDir(dir);
+    }
+    
+    IndexWriter writer = createWriter(target);
+    writer.addIndexes(input);
+    writer.optimize();
+    writer.close();
+
+    verifyIndex(target);
+
+    IOUtils.closeSafely(false, target, input[0], input[1]);
+  }
+  
+  public void testOptimizeAddIndexesReader() throws Exception {
+    Directory[] input = new Directory[] { newDirectory(), newDirectory() };
+    Directory target = newDirectory();
+    
+    for (Directory dir : input) {
+      createDir(dir);
+    }
+    
+    IndexWriter writer = createWriter(target);
+    for (Directory dir : input) {
+      IndexReader r = IndexReader.open(dir);
+      writer.addIndexes(r);
+      r.close();
+    }
+    writer.optimize();
+    writer.close();
+    
+    verifyIndex(target);
+    IOUtils.closeSafely(false, target, input[0], input[1]);
+  }
 }
Index: lucene/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1162001)
+++ lucene/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -4209,8 +4209,6 @@
     merge.readers = new ArrayList<SegmentReader>();
     merge.readerClones = new ArrayList<SegmentReader>();
 
-    merge.info.setHasVectors(merger.fieldInfos().hasVectors());
-
     // This is try/finally to make sure merger's readers are
     // closed:
     boolean success = false;
@@ -4250,6 +4248,9 @@
       // This is where all the work happens:
       mergedDocCount = merge.info.docCount = merger.merge();
 
+      // LUCENE-3403: set hasVectors after merge(), so that it is properly set.
+      merge.info.setHasVectors(merger.fieldInfos().hasVectors());
+
       assert mergedDocCount == totDocCount;
 
       if (infoStream != null) {