Created attachment 107356 [details]
thread dump

Product Version: NetBeans IDE 7.0 Beta 2 (Build 201102140001) 
Java: 1.7.0-ea; Java HotSpot(TM) Client VM 20.0-b04 
System: Windows XP version 5.1 running on x86; Cp1252; en_US (nb) 

Steps:
1. Add a statement that throws an (unimported) exception, e.g.:

import java.io.File;
import java.io.PrintStream;
public class Foo {
    public static void main( String[] args ) {
        new PrintStream(new File("c:/foo"));
    }
}

2. Apply the "add throws clause" hint => deadlock

This is fully reproducible on the aforementioned configuration, but not e.g. on a Win 7 / JDK 6 machine. Attached is a thread dump, seems caused by using Swing components outside of EDT.