Well my main problem with the hammer map editor is when i want to save my map it's seems the hammer save something different, because when i saved the map for example i placed a small edge near the wall but after loading the map the edge got moved or deformed or both by the hammer. This is a very old problem for me (it forced me some years ago to trash some of my mapping project) but it's seems it's still in hammer :\ First time when i saw this problem on my previous computer i suspected this problem to the memory but it's seems thats not the problem because i've got the same issue on this computer aswell.