it sounds like the joints for the hand are already grouped together so basically when you go to scale you are scaling the hand geometry twice - once on it's own and once as a group - which is why the hand exploded. I have seen similar things happen before and it is usually the result of a double transformation due to grouping.

You might want to have a look in the hypershade to see if you have any funny groupings going on. I am no expert though, so I could be way off the mark.