Jeremy C. Reed wrote:

> Is this documented in man page or other official documentation?

yes, rather clearly:

	The error ``Operation not permitted'' may indicate that the
	mount options include privileged options and/or don't include
	options that exclude privileged options. One should try using
	at least ``nodev'' and ``nosuid'' in such cases:

	  mount -t cd9660 -o nodev,nosuid /dev/cd0a /mnt

of course, in this case, the user assumed he "got the permissions
right", so the above wouldn't matter.

-e.