windows - Read Only flag. A property of the folder, too? (not just file objects?)

I select the following option to set the "Read Only" flag at the folder level and to cascade this flag setting to all of the descendant objects...

When I check the files after initiating this command, they of course all have the read only flag set. However, when I check the folder, I see the Read Only flag check box appears in "Mixed state" even though all of the files have the flag set.

I know that Read Only is a property of a file, but is it also a property of a Folder? The Dialog box suggests that it is. However, why is the check box appearing mixed when I display the Read Only property of the folder? All of the files in this folder had there Read Only flag set, so the check box could not be representing a mixed status of the files within the folder.

It looks to me as though this check box is just used as a quick way to cascade the flag setting down, but the dialog box asks me if I "want to set it to the folder only" which confuses me since it does appear to work as though it is a property of the folder.