Changing file permissions?

[va_public <yahoogroups at vikas.mailshell.com>]

I have 2 cron jobs on machine A that do the following: copies a 
directory tree to another disk on the same machine and also copies to 
a remote machine i.e.

0 * * * * rsync -az -delete /disk1/dir/ /disk2/dir
0 * * * * rsync -az -delete /disk1/dir/ machine2:/disk2/dir 

This is workig fine, but every now and then, the file permissions on 
some files in /disk1/dir suddenly lose their 'x' bit

i.e. I do a chmod 774 * on /disk1/dir and after some time, I see that 
the files have permissions as 664!

Would rsync do this? I doubt it but no one else has access to the 
machine and I am at my wits end as to why the permissions would 
suddenly change.