The main(args) entry point cannot be found when a class file has multiple classes and the first class extends another class.

Running the classes shown below results in:
groovy -cp ..\main\groovy ..\main\groovy\MainInvokeSub.groovy
Caught: groovy.lang.GroovyRuntimeException: This script or class could not be run.
It should either:

• have a main method,
• be a JUnit test, TestNG test or extend GroovyTestCase,
• or implement the Runnable interface.

However, if the 'extends MainInvokeBase' is removed or if the second class is commented out, it does run.
The only "spec" I could find about the expected behavior is in the GINA book.

file: MainInvokeBase.groovy
class MainInvokeBase {
}

file: MainInvokeSub.groovy
class MainInvokeSub extends MainInvokeBase{
static main(args)

}

def class SecondClass{
}