This thread, though for EX2, would still apply to Mirror as well, and will probably of use to you. See especially the the post that comes up on clicking the link but read all the posts to find the answer → http://community.wd.com/t5/WD-My-Cloud-EX2/Problem-with-File-Attributes-Permission-on-WD-My-Cloud-EX2/m-p/785209#M1099
If this helps your issue, please click the star under my username on the left of this post to give me a kudo.
