Flash Platform
All AS3 programmers have had to cope with situations where what they can see on the screen is different to what their code is telling them. Within Air, Flex and Flash applications the two main contributors to this are; the Flash Player is single threaded, apart from a few exceptions in Air, and internally is based around a frame rate.

Have you ever tried to measure something you have just added to the Display List and even though you can see it on the screen your measurement, something like width or height, is coming back as 0? How about when you are preloading, does your preloader get stuck at 10% and then jump to 100% at the end?