Re: [Bug-tar] Bug? Where? Why? Why so many files changing as we read them?

[Paul Eggert]

One possibility is that the file system is buggy, and that reading a 
file (and therefore modifying st_atime) also modifies st_ctime as a side 
effect. Often this sort of thing is delayed, that is, you read a file 
and its st_atime is updated immediately, but its st_ctime is updated 
after a delay of a few seconds. This would explain the observed behavior.

See, for example:

https://bugzilla.redhat.com/show_bug.cgi?id=1058526

which does indeed illustrate remote file-system bugs that can cause the 
behavior in question. (Mark O'Keefe's proposed change to tar isn't 
right; there are security reasons to worry about ctime as opposed to mtime).