Underhanded contest: The OS war We all know how the discussion about which is the best operating system caused a lot of flame-wars. Your goal is now, to provide decisive "proof" that your favorite operating system is better... ah, no, much better, to provide decisive "proof" that another operating system is bad.

The task:
Write a program, that does some calculations, and it works correctly on at least one OS and incorrectly on at least another one.


the program should do at least some calculations, so it has to read some simple input (preferably on the standard input, or if from files if you want, but misusing little endian/big endian would not only be cheap, but also obvious), and provide some output depending on the input. The calculations should be meaningful and justified, for example solving a real life or a mathematical problem.
you should specify both operating systems, stating on which one it will work correctly, and on which one it won't. Both operating systems should be well known, and from roughly the same time (so no DOS 1.0 versus a modern OS). It is advised to provide a short description about the cause of the difference (especially if you suspect many people would not realize it) in spoiler tags.



   like this



the cause of the difference has to be subtle, so no #ifdef _WIN32 or similar, please! Remember, your goal is to "prove" that this specific system is bad, so people should not be able to (immediately) spot your trick!
if there is a very strange or very unusual part in your code, you have to justify it in comments why it is there. Of course, this "justification" can/will be a big lie.


Scoring:

This is not a golf! The code should be well organized, and kept simple. Remember, your goal is to hide a bug into it so that people won't suspect it. The simpler the code, the less suspicious it is.

The winner will be decided by votes. The most votes after approximately 10 days after the first valid submission wins. Generally, answers where the code is easy to read and understand, yet the bug is well hidden, and even if discovered, can be attributed to a mistake rather than malice, should be voted up. Similarly, it should be worth much more if the bug just causes an incorrect result, rather than just causing the program to crash or to not do anything.

As usual, I withhold the right to choose an answer as a winner if it is not more than either 10% or 1 point below the one with the most votes, on any subjective criteria.
Python

This program opens the image specified on the command line and displays it.

import Image
import sys

with open(sys.argv[1]) as f:
    im = Image.open(f)
    im.show()


Works on linux, does not work on windows. 

This is due to the way windows opens files. Binary mode must be specified for this to work properly on all operating systems.