Index: lucene/core/src/java/org/apache/lucene/index/IndexFileDeleter.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexFileDeleter.java	(revision 1357246)
+++ lucene/core/src/java/org/apache/lucene/index/IndexFileDeleter.java	(working copy)
@@ -149,7 +149,8 @@
 
     for (String fileName : files) {
 
-      if (!fileName.endsWith("write.lock") && !fileName.equals(IndexFileNames.SEGMENTS_GEN)) {
+      if (!fileName.endsWith("write.lock") && !fileName.equals(IndexFileNames.SEGMENTS_GEN)
+          && (fileName.startsWith("_") || fileName.startsWith(IndexFileNames.SEGMENTS))) {
 
         // Add this file to refCounts with initial count 0:
         getRefCount(fileName);
Index: lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java	(revision 1357246)
+++ lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java	(working copy)
@@ -253,15 +253,28 @@
   public void setFiles(Set<String> files) {
     setFiles = files;
     sizeInBytes = -1;
+    assertSaneFileNames();
   }
 
   public void addFiles(Collection<String> files) {
     setFiles.addAll(files);
+    sizeInBytes = -1;
+    assertSaneFileNames();
   }
 
   public void addFile(String file) {
     setFiles.add(file);
+    sizeInBytes = -1;
+    assertSaneFileNames();
   }
+  
+  // used only by assert
+  private boolean assertSaneFileNames() {
+    for (String file : setFiles) {
+      assert file.startsWith("_") : "invalid codec filename: " + file ;
+    }
+    return true;
+  }
     
   /**
    * Get a codec attribute value, or null if it does not exist
Index: lucene/core/src/test/org/apache/lucene/index/TestDoc.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestDoc.java	(revision 1357246)
+++ lucene/core/src/test/org/apache/lucene/index/TestDoc.java	(working copy)
@@ -125,13 +125,13 @@
       printSegment(out, si2);
       writer.close();
 
-      SegmentInfoPerCommit siMerge = merge(directory, si1, si2, "merge", false);
+      SegmentInfoPerCommit siMerge = merge(directory, si1, si2, "_merge", false);
       printSegment(out, siMerge);
 
-      SegmentInfoPerCommit siMerge2 = merge(directory, si1, si2, "merge2", false);
+      SegmentInfoPerCommit siMerge2 = merge(directory, si1, si2, "_merge2", false);
       printSegment(out, siMerge2);
 
-      SegmentInfoPerCommit siMerge3 = merge(directory, siMerge, siMerge2, "merge3", false);
+      SegmentInfoPerCommit siMerge3 = merge(directory, siMerge, siMerge2, "_merge3", false);
       printSegment(out, siMerge3);
       
       directory.close();
@@ -160,13 +160,13 @@
       printSegment(out, si2);
       writer.close();
 
-      siMerge = merge(directory, si1, si2, "merge", true);
+      siMerge = merge(directory, si1, si2, "_merge", true);
       printSegment(out, siMerge);
 
-      siMerge2 = merge(directory, si1, si2, "merge2", true);
+      siMerge2 = merge(directory, si1, si2, "_merge2", true);
       printSegment(out, siMerge2);
 
-      siMerge3 = merge(directory, siMerge, siMerge2, "merge3", true);
+      siMerge3 = merge(directory, siMerge, siMerge2, "_merge3", true);
       printSegment(out, siMerge3);
       
       directory.close();
Index: lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 1357246)
+++ lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -45,6 +45,7 @@
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.store.Lock;
 import org.apache.lucene.store.LockFactory;
 import org.apache.lucene.store.LockObtainFailedException;
@@ -1799,4 +1800,23 @@
     r.close();
     dir.close();
   }
+  
+  //LUCENE-1468 -- make sure opening an IndexWriter with
+  // create=true does not remove non-index files
+  
+  public void testOtherFiles() throws Throwable {
+    Directory dir = newDirectory();
+    try {
+      // Create my own random file:
+      IndexOutput out = dir.createOutput("myrandomfile", newIOContext(random()));
+      out.writeByte((byte) 42);
+      out.close();
+      
+      new IndexWriter(dir, newIndexWriterConfig( TEST_VERSION_CURRENT, new MockAnalyzer(random()))).close();
+      
+      assertTrue(dir.fileExists("myrandomfile"));
+    } finally {
+      dir.close();
+    }
+  }
 }