diff --git a/zanata-war/src/main/java/org/zanata/ui/model/statistic/MessageStatistic.java b/zanata-war/src/main/java/org/zanata/ui/model/statistic/MessageStatistic.java
index dd36ab96f2..41e335dfee 100644
--- a/zanata-war/src/main/java/org/zanata/ui/model/statistic/MessageStatistic.java
+++ b/zanata-war/src/main/java/org/zanata/ui/model/statistic/MessageStatistic.java
@@ -5,6 +5,8 @@
  */
 public class MessageStatistic extends AbstractStatistic {
 
+    private static final long serialVersionUID = 1L;
+
     public MessageStatistic() {
         super();
     }
diff --git a/zanata-war/src/main/java/org/zanata/ui/model/statistic/WordStatistic.java b/zanata-war/src/main/java/org/zanata/ui/model/statistic/WordStatistic.java
index 640883b551..ad99f8fa5f 100644
--- a/zanata-war/src/main/java/org/zanata/ui/model/statistic/WordStatistic.java
+++ b/zanata-war/src/main/java/org/zanata/ui/model/statistic/WordStatistic.java
@@ -8,6 +8,8 @@
  */
 public class WordStatistic extends AbstractStatistic {
 
+    private static final long serialVersionUID = -8807499518683834883L;
+
     @Getter
     @Setter
     private double remainingHours;
diff --git a/zanata-war/src/test/java/org/zanata/ZanataJpaTest.java b/zanata-war/src/test/java/org/zanata/ZanataJpaTest.java
index bdd7453c24..0c8c171ebb 100644
--- a/zanata-war/src/test/java/org/zanata/ZanataJpaTest.java
+++ b/zanata-war/src/test/java/org/zanata/ZanataJpaTest.java
@@ -6,6 +6,7 @@
 import javax.persistence.EntityManagerFactory;
 import javax.persistence.Persistence;
 
+import net.sf.ehcache.CacheManager;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.junit.After;
@@ -23,7 +24,8 @@
 import org.zanata.testng.TestMethodListener;
 
 @Listeners(TestMethodListener.class)
-@Test
+// single threaded because of ehcache (perhaps other reasons too)
+@Test(singleThreaded = true)
 public abstract class ZanataJpaTest {
     private static final Logger log = LoggerFactory.getLogger(ZanataJpaTest.class);
     private static final String PERSIST_NAME = "zanataTestDatasourcePU";
@@ -36,6 +38,7 @@ public abstract class ZanataJpaTest {
     @Before
     protected void setupEM() {
         log.debug("Setting up EM");
+        CacheManager.getInstance().clearAll();
         em = emf.createEntityManager();
         em.getTransaction().begin();
     }
@@ -50,6 +53,7 @@ protected void shutdownEM() {
             em.close();
         }
         em = null;
+        CacheManager.getInstance().clearAll();
     }
 
     protected EntityManager getEm() {
diff --git a/zanata-war/src/test/java/org/zanata/rest/service/TranslationResourceRestTest.java b/zanata-war/src/test/java/org/zanata/rest/service/TranslationResourceRestTest.java
index eee215bcfc..5c32fbc863 100644
--- a/zanata-war/src/test/java/org/zanata/rest/service/TranslationResourceRestTest.java
+++ b/zanata-war/src/test/java/org/zanata/rest/service/TranslationResourceRestTest.java
@@ -84,6 +84,7 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+// single threaded because of ehcache (perhaps other reasons too)
 @Test(singleThreaded = true)
 public class TranslationResourceRestTest extends ZanataRestTest {
     private static final Logger log = LoggerFactory