Time Machine and incremental backups

I have been able to set up My World Book II so that it is recognised by the Time Machine.  Howeve rit only seems to perform full backups every time it runs which means it backs up 20+ GB every time (it is a new Mac and so there is not much on it so far).  I am told by Apple Support that this means there is a problem with the hard drive but since it is only  a few weeks old and seems to be recognised by the Mac this seems fine.  It backs up a full back up every time with no problems  i assume there is a problem with the set up.  I would be grateful for any ideas.

Hello friend did you ever get this issue resolved?