i love bethesda, but....
Skyrim has MANY glitches. people have been killed by walking into a cart!!! (the cart accelerates away, bounces off and speeds up.... and MURDERS you). people have fallen INTO cliffs, people "sit" in the air next to chairs, tables, beds..... people jumping off a small cliff and falling through the ground for some time before dying... horses fast traveling INTO cities, and being stuck there... torches vanishing, but still casting light... shadows appearing when there is nothing/noone there....
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its a given. bethesda has glitches...
go to skyrim.nexusmods.com and look for unofficial skyrim patch (they have those for dlc as well as main game).. it fixes some of the glitches, errors and mistakes....