Unix systems and Macs use the ctime, also called the inode change time, to store the time a file's attributes were last changed. That ctime stamp is updated each time when for instance the owner or the posix access rights of a file change.

PresSTORE Backup always honors a change to the file attributes.
PresSTORE Synchronize honors a change to the file attributes when in

Sync Plan -> Additional Options -> Expert Settings

the flag

Compare source and target files by examining:  ... Owner and/or protection changes ...  

is set.

On Windows, the file attributes have been reinvented: There is a ctime stamp on Windows, but it reflects the file creation time. Changes to the file's ownership or access rights do not update a time stamp but set an archive bit that is intended to be unset by backup software.

PresSTORE honors the archive bit and unsets it on the source and sets a time stamp on the same file in an alternate data stream (ADS). This has been done for two reasons:

• To overcome a time gap in case the archive bit is set while a file is saved

• To enable the same handling of files on Windows and Unix

This may cause as side effect that a changed file on Windows is saved twice in case PresSTORE cannot safely decide whether the file has been changed before or after being read (remember that file reading takes a time interval, during which the archive bit might be set again).

Please also see this very good blog article on this topic by Florian Bogner:

http://bogner.sh/?p=180