This one isn't so much as a game glitch as it is a map glitch.
I usually play on a map with one of my characters. Beautiful, beautiful map. Absolutely gorgeous. Now, I'm a "mod" on this server/group, so I'm on a lot. I eventually get on once I wake, and this glitch goes unnoticed for a few hours. Once I begin to f3 around, however, I find it. A large forest of giant, pure white, pine trees. They were absolutely everywhere. Sticking out of the camps like giant blades of grass, but instead they were that milky white color you see when people have a markings pack you don't have, and they were also trees. It was absolutely horrifying.