Steven,
as far as I know, ADSM checks size, all attributes (except archive bit and
last read access) and the security entries of each file to decide whether to
do a backup or not. So when you change the permissions of a file it will get
backed up.
One might think it to be better just to update the security entries in such
case, but what if a change in security entries is the information you want
to undo? So you need some versioning also for the attributes and ADSM simply
takes the whole file...

Regards,
Michael