Remote service exception checked, translated into StatusCodeException in tomcat

I have a GWT application that makes normal RPC calls for RemoteService, whose methods can throw a ServiceException:

public class ServiceException extends Exception implements java.io.Serializable {
    private static final long serialVersionUID = 1L;
    public ServiceException() {}
    public ServiceException(final Throwable cause) {
        super(cause);
    }
    public ServiceException(final String errorMsg) {
        super(errorMsg);
    }
}

This works fine in design mode, where I get the expected exception messages in my onFailure async callback, but when I compile the application and deploy it to tomcat, my exception translates to

com.google.gwt.user.client.rpc.StatusCodeException: 500 The call failed on the server; see server log for details

As in dev mode, my server logs show the expected reason for the exception that I registered just before throwing a ServiceException.

I searched this on google but couldn't find anything relevant.

(I am working on Mac OS X Lion with GWT 2.4, java 1.6 and Tomcat 7.0.16)