Cubby was having the same problem. You might want to do a seach and find the post on it - it was relatively recent. I know they put him on medication which was recently discontinued because it was totally altering his personality.

I know Tubby did this when he was young also, but he had one of my slippers for a "friend" instead of my leg, and it wasn't constant so I never really thought of it as a problem. Maybe if you can distract him when he starts, or do the "NO" thing like you do if he does something wrong....