copy VersionedValue before returning to protect internal state

Change-Id: If56c512488b90bbfbabe32434e567b463d4acf1a
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
index 6d8d5bd..d132b7c 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
@@ -76,7 +76,7 @@
                 results.add(new InternalReadResult(InternalReadResult.Status.NO_SUCH_TABLE, null));
                 continue;
             }
-            VersionedValue value = table.get(request.key());
+            VersionedValue value = VersionedValue.copy(table.get(request.key()));
             results.add(new InternalReadResult(
                     InternalReadResult.Status.OK,
                     new ReadResult(