Weird any ideas?

I have just been replacing my sills and the rear mounting points. Got one done fine but the other the bolt seemed to short, i must have spent ages lowering the body down wondering why it would not fit them i noticed the sleeve on the bracket on the chassis on one side is slightly longer than the other side! I thought about cutting it but didnt want to do any cutting to the chassis in the end i just got a longer bolt - then ran out of welding gas. Anyway any ideas why this is? or was the guy building my disco just badly hungover?

a pciture would be useful