This applies to both survival and creative. When a normal train track is put adjacent/next to a snow-covered block, the track gets snow beneath it! When the normal track is removed, the snow disappears too. I never placed snow on the track anyway. This was using a Bukkit server, but applies to vanilla single-player as well.
Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.