It's not a permissions error and you are not seeing things. It's a Preview bug.
Thanks for your view on the issue. While at first glance the permissions repair might be considered instrumental, in all cases I can assess Preview was also quit and reloaded, and hence remained a contender for mischief. Of course, there’s also the observation of 3rd party apps that had no problems loading the files Preview balked at. Like you, I have seen Preview misbehave occasionally for quite a while, but the inconsistence of that behavior camouflaged its potential involvement.
