Man vs. Computer

I decided against re specifying my model after I realized I had a bug in my program that was completely throwing of my estimates. So now everything is working, however I have ran into a very annoying problem that happens every so often. A theoretical result that I absolutely know is true is not being verified by my computer. I have programmed long enough to know that 99% of the time, there is an error in either my logic or what I am programming and not the computer and so the fact that I can't correct the problem is quite frustrating

A simple example of the problem I am facing that I know for a fact that (x-2)^2=x^2-2x+4

Yet when I have my computer compute: (x-2)^2

I get a different value than: x^2-2x+4

Even more frustrating is when I generate my data one way, I get same number in both equations; it's just when I generate the data using another way.

I cannot for the life of me figure out what I am doing wrong, I have been staring at this for hours and almost embarrassed to have to ask my adviser about this. Sometimes when you stare at a problem so long, the simple things become the problems. I really should be quite thrilled about having obtained good estimates of all the parameters, but this is really clouding my high.