Rear n/s tyre strangeness

[Big G]

The mrs has bought a 03 mk4 golf in white (finally lol)

The rear o/s tyre is worn on the inside and outside, but the middle is above legal depth. She plans to swap the wheels and tyres anyway, but if there is an underlying problem it would be good to know about it before it eats another tyre.

also after driving on it it is warm to touch. the other 3 tyres are cold. she doesn't hammer it everywhere and I thought it was most strange the 1 tyre is hot and the other isn't.

any ideas?