behavior of Groovyshell and GroovyScriptEngine is not similar

I embedded groovy in my java application and tried to run the short script below.

import java.lang.Thread
import java.lang.Runnable

t = new Thread()

t.start()
t.join()

I embedded groovy first with the Groovyshell and the Result is as expected (Console output "Hi")

Binding binding = new Binding();
GroovyShell shell = new GroovyShell(binding);
String[] test=null;
Object result = shell.run(new File(path+"/"+file), test);

The second try was with the GroovyScriptEngine:

String[] roots = new String[]

;
GroovyScriptEngine gse = new GroovyScriptEngine(roots);
Binding binding = new Binding();
gse.run(file, binding);

In this case I got a exception:
groovy.lang.MissingMethodException: No signature of method t.start() is applicable for argument types: () values: {}
at groovy.lang.MetaClassImpl.invokeStaticMethod(MetaClassImpl.java:507)
at org.codehaus.groovy.runtime.Invoker.invokeMethod(Invoker.java:138)
at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:104)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethod(ScriptBytecodeAdapter.java:85)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeNoArgumentsMethod(ScriptBytecodeAdapter.java:175)

I don't know if it is really a bug.