diff --git a/src/java/org/apache/lucene/index/SegmentReader.java b/src/java/org/apache/lucene/index/SegmentReader.java
--- a/src/java/org/apache/lucene/index/SegmentReader.java
+++ b/src/java/org/apache/lucene/index/SegmentReader.java
@@ -652,7 +652,8 @@
     }
 
     // if we're cloning we need to run through the reopenSegment logic
-    if (normsUpToDate && deletionsUpToDate && !doClone && openReadOnly == readOnly) {
+    // also if both old and new readers aren't readonly, we clone to avoid sharing modifications
+    if (normsUpToDate && deletionsUpToDate && !doClone && openReadOnly && readOnly) {
       return this;
     }    
 
diff --git a/src/test/org/apache/lucene/index/TestIndexReaderReopen.java b/src/test/org/apache/lucene/index/TestIndexReaderReopen.java
--- a/src/test/org/apache/lucene/index/TestIndexReaderReopen.java
+++ b/src/test/org/apache/lucene/index/TestIndexReaderReopen.java
@@ -1160,21 +1160,20 @@
 
   public void testDeletes() throws Throwable {
     Directory dir = new MockRAMDirectory();
-    createIndex(dir, false);
-    // Get delete bitVector
-    modifyIndex(0, dir);
-    IndexReader r1 = IndexReader.open(dir);
+    createIndex(dir, false); // Create an index with a bunch of docs (1 segment)
 
-    // Add doc:
-    modifyIndex(5, dir);
+    modifyIndex(0, dir); // Get delete bitVector on 1st segment
+    modifyIndex(5, dir); // Add a doc (2 segments)
 
-    IndexReader r2 = r1.reopen();
+    IndexReader r1 = IndexReader.open(dir); // MSR
+
+    modifyIndex(5, dir); // Add another doc (3 segments)
+
+    IndexReader r2 = r1.reopen(); // MSR
     assertTrue(r1 != r2);
 
-    IndexReader[] rs2 = r2.getSequentialSubReaders();
-
-    SegmentReader sr1 = (SegmentReader) r1;
-    SegmentReader sr2 = (SegmentReader) rs2[0];
+    SegmentReader sr1 = (SegmentReader) r1.getSequentialSubReaders()[0]; // Get SRs for the first segment from original
+    SegmentReader sr2 = (SegmentReader) r2.getSequentialSubReaders()[0]; // and reopened IRs
 
     // At this point they share the same BitVector
     assertTrue(sr1.deletedDocs==sr2.deletedDocs);