Archive Attribute Won't Be Removed

[un_ungherese]

I would like to use zg.exe for incremental backup through the option I1, but it doesn't work:

zg -add test.zip I1 +"C:\My Folder\*.*" doesn't remove the archive attribute.

Another thing I have noticed:

zg -add test.zip +"C:\My Folder\*.*" doesn't zip files with the hidden attribute set.

And a question:

What can "zg -backup" that "zg -add" can't? It seems -backup can nor yet less than -add (much less options).

Thanks.