Java - Platform Independent, so why different results?

Question

This isn't a code specific topic, but I hope someone can still help me out with this. I've been developing a bit of code for a Java class that I'm taking, working in a small group with a few friends. I spend an entire weekend pounding out a GUI for this project, and upon completion, test it thoroughly and agressively, absolutely TRYING to get it to crash. Once I'm satisified it's got more safety features than a Volvo, I pass it along to my friend and ask him to play with it a little and see what happens.
Well, suffice to say he gets COMPLETELY different results. The layout of the GUI is the same, but on his side, when the code executes to remove a JLabel, it removes a couple of others with it. Upon staring at my code for hours, doing handwritten walk-throughs of the code itself, and doing more staring at the code, I can't understand for the life of me what's causing this. On my side, the one JLabel disappears just fine, reappears when the code is executed to restore it. On his side, multiple JLabels disappear, and refuse to reappear.
I've tried changing it from setting them to disappear to setting them to setText("") and turn white. The same thing happens... multiple JLabels turn white and remove their text.
The only common denominator I can get out of this is that his machines (he's tested more than one) are all multi-core systems (dual core or quad core), where mine is single core. Even then, I see nothing in the code that even if it were threaded should cause this to happen. The functions are extremely specific. Still, I'll confess to not knowing a THING about threading, could this have something to do with it? I can post some code if that would help, but there's quite a bit of it...

Answer 1

I don't currently have my code available, but I've got a pseudocode outline of what's supposed to be happening, if that will help any... if not, sorry for just cluttering things up... >_>
In response to the JLabel array quesiton, I have an X x Y sized grid made of JLabels, dynamically drawn based on user input (how many rows and how many columns they want). While those are in an array, they're not involved in this part of the process...
The way this works is the project is a simulation of an assembly line on a shop floor. There are four types of mahcines, called BodyAttacher, Painter, InteriorAssembler, Wrapper, and Conveyor. There can only be one BodyAttacher, Painter, InteriorAssember, and Painter. Conveyors are essentially unlimited. There is a JLabel for each of these machines labeled with the name of that machine. Each one is setText to their class name. To ensure the user can ONLY place one of the first four machines, the code below kicks in. For simplicity's sake, I've included only the mouselistener for the BodyAttacher and the function that it calls, because they all do the same thing (except for a different instance of a machine).
The method that happens when the user does this goes like this:
//      This is done from memory, and I couldn't remember all of the code
//      exactly, so any parts that have glaring errors (like the name of the
//      mouse listener and the reference to event) because these probably
//      aren't right.
Machine newMachine = null;  // this is used to hold new machines as they are
                                           // created before they are attached to the line.
// This is the mouse listener for the BodyAttacherLabel
public void BodyAttacherLabelMouseClicked(java.awt.event evt) {
         JLabel tempMachineLabel = evt.getSource();  // store the source of which label was clicked on.
         if (tempMachineLabel.isEnabled()) {
                 newMachine = new BodyAttacher();
                 disableMachineLabel(tempMachineLabel);
         tempMachineLabel = null;   // ensure no other calls accidentally access this label
// This is the method to disable the button
public void disableMachineLabel(Label temp) {
        temp.setEnabled(false);
        temp.setText("");
}This was done from memory, and probably isn't even syntactically correct but it gives an idea of how this works. Could screwy threading be causing disableMachineLabel to execute on more than one Label or something? I can't imagine why or how it would, but I don't know much about threading...