If you need your stem that short your frame clearly doesn't fit you but that's not the end of the world. And since most of the newish fixed gear folk have never been properly fitted for a frame, you are not alone, including myself. Most are lucky if their frames come close to fitting. If the 50mm stem helps to make your bike fit then great. Some folks set up their bikes to internet photo aesthetics and when they ride their bikes they look like jackasses.