Wayne
Maybe not but reported in the Microsoft answers:
Some programs may display error messages when you try to save files to a folder that uses the Read-only or System attribute. As a result, these programs may not be able to save files to the folder.
I agree with you that with a dot in the box it does not mean that a file is r/o - a tick would show that (?). But if a file is definitely r/o then it can cause the problems stated above.
Possibly the only sure way to make sure a file is really/correctly read-write is to use a command-line prompt and/or remove the read-only setting via a command prompt: attrib -r +s drive:\<path>\<foldername>, and then only if you have issues writing to files.
Sometimes the disk-write error in steam is due to the r/o attribute.
pH