Mesh deforms terribly in game, why?

I am trying to convert some boots. They look fine in Blender, and the weights also seem to work fine in Blender, but for some reason they deform very badly in game.
This is what they look like in game:



I even tried to import/export from S4Studio and transfer the weights a second time because I know sometimes they get messy in S4Studio, but no luck.

Here is the .blend file.

If anyone can check it and try to see if anything is wrong with the mesh/weights, I would appreciate it!