Index: lucene/src/java/org/apache/lucene/index/DirectoryReader.java
--- lucene/src/java/org/apache/lucene/index/DirectoryReader.java	Sun Dec 05 19:21:44 2010 -0500
+++ lucene/src/java/org/apache/lucene/index/DirectoryReader.java	Mon Dec 06 19:51:46 2010 -0500
@@ -770,6 +770,7 @@
                                                       deletionPolicy == null ? new KeepOnlyLastCommitDeletionPolicy() : deletionPolicy,
                                                       segmentInfos, null, null, codecs);
       segmentInfos.updateGeneration(deleter.getLastSegmentInfos());
+      segmentInfos.changed();
 
       // Checkpoint the state we are about to change, in
       // case we have to roll back:
Index: lucene/src/java/org/apache/lucene/index/IndexWriter.java
--- lucene/src/java/org/apache/lucene/index/IndexWriter.java	Sun Dec 05 19:21:44 2010 -0500
+++ lucene/src/java/org/apache/lucene/index/IndexWriter.java	Mon Dec 06 19:51:46 2010 -0500
@@ -741,6 +741,7 @@
         // Record that we have a change (zero out all
         // segments) pending:
         changeCount++;
+        segmentInfos.changed();
       } else {
         segmentInfos.read(directory, codecs);
 
@@ -757,6 +758,7 @@
           oldInfos.read(directory, commit.getSegmentsFileName(), codecs);
           segmentInfos.replace(oldInfos);
           changeCount++;
+          segmentInfos.changed();
           if (infoStream != null)
             message("init: loaded commit \"" + commit.getSegmentsFileName() + "\"");
         }
@@ -774,12 +776,14 @@
                                      conf.getIndexDeletionPolicy(),
                                      segmentInfos, infoStream, docWriter, codecs);
 
-      if (deleter.startingCommitDeleted)
+      if (deleter.startingCommitDeleted) {
         // Deletion policy deleted the "head" commit point.
         // We have to mark ourself as changed so that if we
         // are closed w/o any further changes we write a new
         // segments_N file.
         changeCount++;
+        segmentInfos.changed();
+      }
 
       docWriter.setMaxBufferedDeleteTerms(conf.getMaxBufferedDeleteTerms());
       docWriter.setRAMBufferSizeMB(conf.getRAMBufferSizeMB());
@@ -1537,6 +1541,7 @@
       // name that was previously returned which can cause
       // problems at least with ConcurrentMergeScheduler.
       changeCount++;
+      segmentInfos.changed();
       return "_" + Integer.toString(segmentInfos.counter++, Character.MAX_RADIX);
     }
   }
@@ -2119,6 +2124,7 @@
    */
   private synchronized void checkpoint() throws IOException {
     changeCount++;
+    segmentInfos.changed();
     deleter.checkpoint(segmentInfos, false);
   }
 
@@ -3686,6 +3692,7 @@
             }
             toSync.remove(toSync.size()-1);
             changeCount++;
+            segmentInfos.changed();
           }
         }
         assert filesExist(toSync);
Index: lucene/src/java/org/apache/lucene/index/SegmentInfos.java
--- lucene/src/java/org/apache/lucene/index/SegmentInfos.java	Sun Dec 05 19:21:44 2010 -0500
+++ lucene/src/java/org/apache/lucene/index/SegmentInfos.java	Mon Dec 06 19:51:46 2010 -0500
@@ -862,4 +862,10 @@
     }
     return count;
   }
+
+  /** Call this before committing if changes have been made to the
+   *  segments. */
+  public void changed() {
+    version++;
+  }
 }