Skyrim Dawnguard under map glitch appears

Product-Reviews writes: After installing the Skyrim Dawnguard DLC we went to Whiterun to meet a guard, which is how you start a trigger for the Fort Dawnguard quest, and we met a certain bug for the first time on our Xbox 360. When we walked towards the blacksmith hut we noticed the ground had gone where you normally start smithing, and then guards started falling under the map. This glitch only happened after installing the Dawnguard DLC and running the latest patch.