Product Version: NetBeans IDE Dev (Build 201110050601)
Java: 1.7.0_147-icedtea; OpenJDK Client VM 21.0-b17
System: Linux version 3.0.0-1-686-pae running on i386; UTF-8; en_US (nb)

1) Open Java Editor and create the following class
2) Have some changes in the Undo history so the Undo button is enabled

class Test {
    public void test() {
        final String s;

        s = init();

        System.out.println(s);
    }

    private String init() {
        return "a";
    }
}

3) Place the cursor on the init() method and invoke Refactor->Inline...
4) Preview window is shown and Undo button is grayed out

5a) Cancel the refactoring will re-enable the Undo button

5b) Execute the refactoring will cause the Undo history to be truncated and the Undo button stays grayed out