after upgrading to openssh-7.5p1, trying to use -i on local keys fails:
Loading NaCl plugin... done.
Load key "/.ssh/id_rsa": file changed while reading
Permission denied (publickey).

this is because in our fstat stub, we just zero out the stat structure.  then when openssh runs, it does:
authfile.c:
int
sshkey_load_file(int fd, struct sshbuf *blob)
{   
...
    if ((st.st_mode & S_IFREG) == 0 || st.st_size <= 0) {
        debug("bumping stat size to 64KiB\n");
        st.st_size = 64*1024; /* 64k should be enough for anyone :) */
        dontmax = 1;
    }
...
    if ((st.st_mode & (S_IFSOCK|S_IFCHR|S_IFIFO)) == 0 &&
        st.st_size != (off_t)sshbuf_len(blob)) {
        debug("mode:%x size:%lli len:%zu\n", st.st_mode, st.st_size, sshbuf_len(blob));
        r = SSH_ERR_FILE_CHANGED;
        goto out;
    }
...

so in our case, it sees the stat size is 0, so it ups to 64KiB, and then later complains when the amount of key data it read wasn't 64KiB.