Nautilus ACL MASK is Not in Sync With Group Permissions (6464485)

The Group permissions in the Permissions tab should be the same as the Mask permissions in the Access Tab, but on some occasions they appear out of sync.

Workaround: Click the Close button, and then click Reload. View the file properties again. The Group permissions and the Mask permissions will now be in sync again. The permissions are set to what you changed the Mask to in the previous step.