A possible bug with Netbeans, it's executing the old code I changed

Question

I have been coding in a project with over 500 class. One of the classes is responsible for retreiving data from the disk. For some reasons I changed the code, but still, when I run the code, it executes the old code of the class. When I debug, the debugger moves over empty lines which means it still runs over the old code that I have changed. I cleaned and built the project several times. I hand deleted all the .class files and built the project again and nothing changed.

What drives me crazy, is that I copy-paste this code to a new class in a new project and I test it using a main method within the class it works just fine.

I guess it's a bug in netbeans or there is something behind that i don't know about. The version I'm using is 7.1 and it's up to date.

Any idea of how to overcome this ?