Emulation class which extends JavaScriptObject cause IncompatibleClassChangeError Exception on module load in development mode

[babyeric]

Issue Report Summary: Emulation class which extends JavaScriptObject
cause IncompatibleClassChangeError Exception on module load in
development mode


Found in GWT Release:
GWT 2.3.0


Encountered on OS / Browser:
Win7, IE6-8, Chrome, hosted mode


Detailed description:
step to reproduce:
1. create a new starter GWT project, e.g. testEmul
2. add a emulation class "Calendar" to the project
folder structure can be:

TestEmul
TestEmul.gwt.xml
client
shared
server
emul
java
util
Calendar.java

3. add super-source tag to TestEmul.gwt.xml
<super-source path='emul' />
4. launch project in development mode

see exception:
22:07:23.238 [ERROR] [testemul] Unable to initialize static dispatcher

java.lang.IncompatibleClassChangeError: Implementing class
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at
com.google.gwt.dev.shell.CompilingClassLoader.findClass(CompilingClassLoader.java:
1078)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at com.google.gwt.dev.shell.JsValueGlue.set(JsValueGlue.java:220)
at
com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:
127)
at
com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:
561)
at
com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:
289)
at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:
332)
at
com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:
193)
at
com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:
510)
at
com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:
352)
at java.lang.Thread.run(Unknown Source)

Shortest code snippet which demonstrates issue:
//Calendar.java
package java.util;
import com.google.gwt.core.client.JavaScriptObject;
public final class Calendar extends JavaScriptObject {
protected Calendar() {
}
}