RPC Error after GWT 2.3 upgrade

Question

After upgrading to GWT 2.3 some of my RPC services no longer work and fail with "The response could not be deserialized". It seems to happen to services that are returning objects that are use Date objects that are annotated with @Temporal(TemporalType.TIMESTAMP). I use Gilead 1.3.2 and Hibernate 3.6 and I had no issues with GWT 2.2. Any idea what could be going on, or how to start debugging?

Here's the stack trace:

com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException: The response could not be deserialized
  at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:221)
  at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java: 287)
  at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:395)
  at sun.reflect.GeneratedMethodAccessor33.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImp l.java:25)
  at java.lang.reflect.Method.invoke(Method.java:597) 
  at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
  at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
  at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:167)
  at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:326)
  at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:207)
  at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:132)
  at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
  at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
  at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
  at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
  at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
  at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:214)
  at sun.reflect.GeneratedMethodAccessor27.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:597)
  at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
  at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
  at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:167)
  at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:281)
  at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:531)
  at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:352)
  at java.lang.Thread.run(Thread.java:680)
Caused by: com.google.gwt.user.client.rpc.SerializationException: java.sql.Timestamp/1769758459
Caused by: com.google.gwt.user.client.rpc.SerializationException: java.sql.Timestamp/1769758459
  at com.google.gwt.user.client.rpc.impl.SerializerBase.getTypeHandler(SerializerBase.java:153)
  at com.google.gwt.user.client.rpc.impl.SerializerBase.instantiate(SerializerBase.java:114)
  at com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader.deserialize(ClientSerializationStreamReader.java:111)
  at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamReader.readObject(AbstractSerializationStreamReader.java:119)
  at com.lensoo.shared.entity.Course_FieldSerializer.deserialize(Course_FieldSerializer.java:320)
  at com.lensoo.shared.entity.Course_FieldSerializer.deserial(Course_FieldSerializer.java:405)
  at com.google.gwt.user.client.rpc.impl.SerializerBase.deserialize(SerializerBase.java:95)
  at com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader.deserialize(ClientSerializationStreamReader.java:113)
  at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamReader.readObject(AbstractSerializationStreamReader.java:119)
  at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter$ResponseReader$8.read(RequestCallbackAdapter.java:106) 
  at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:214)
  ... 26 more 
  ... 26 more