Nearly every mini i've followed does this!
Thats because the rear end of the Mini is narrower than the front, you are sitting one one side in the car following so you see more of one side.
Its an optical illusion.
General perception tells you that the front should be narrower than the back because its further away, your brain gets confused and it looks like its crabbing when its not.
However this actaul crabbing is common. Iv never had a mini thats had the toe setting on the rear the same side to side. It can be worse with some pattern subframes, they are pants when it comes to line them up. It can be any number of things as said before.