How can a bug could occur on static, fixed input data only "sometimes"? The following is simply an example I have observed, but I am not interested in an answer specific to the GD library.
I have some PHP code to render SVG files, utilizing the GD Graphics library. It often stops working, and no error is given. The strange thing is that after 2-3 tries it works and keeps working with no code changes. This is very strange to me because I understand that assembled code follows in sequential order and operates on certain external inputs. In this case, the known input is a static file.
My question is, how is this possible (from a general, theoretical point of view)? What could the GD library (or any other code) be doing to cause such irregular behavior? How could code run differently based on how many times you ran it, if the input stayed the same?