Usually issues will be reproduce-able. The code isn't changing each time you submit the form, so the issue is either with what you are entering into the form or the way you are navigating to it that isn't consistent.
The key to tracking down a problem is being able to reproduce it. If you give me a url where I can see the issue and FTP access I can try to reproduce and debug it. The first thing I'd do is figure out steps I can take to actually see the problem. From there it is usually pretty easy to determine what you did wrong.