1. Create simple java class:

class Class_A {
    class Super {
        public void m1() {
            int x;
            int y = 3;
        }
    }
   
    class Sub extends Super {
        public void m1() {
            int x = 3;
        }
    }
}

2. Select "int x = 3;" and using Alt+Shift+P invoke Introduce Parameter dialog

3. Uncheck all checkboxes and select "Update Existing Method", then press Refactor 

>> Without any warning you'll get incompilable code since variable "x" is already defined in "Super.m1()"

class Class_A {
    class Super {
        public void m1(int x) {
            int x;
            int y = 3;
        }
    }
    
    class Sub extends Super {
        public void m1(int x) {
        }
    }
}

Product Version: NetBeans IDE Dev (Build 201310290001)
Java: 1.7.0_45; Java HotSpot(TM) 64-Bit Server VM 24.45-b08
Runtime: Java(TM) SE Runtime Environment 1.7.0_45-b18
System: Windows 7 version 6.1 running on amd64; Cp1252; en_US (nb)