Debug, and review the code of exportfs,
find that: this is a bug of exportfs(also about kernel):

static int test_export(char *path, int with_fsid)
{
        char buf[1024];
        int fd, n;

        sprintf(buf, "-test-client- %s 3 %d -1 -1 0\n",
                path,
                with_fsid ? NFSEXP_FSID : 0);
        fd = open("/proc/net/rpc/nfsd.export/channel", O_WRONLY);
        if (fd < 0)
                return 0;
        n = write(fd, buf, strlen(buf));
        close(fd);
        if (n < 0)
                return 0;
        return 1;
}

1. if the path is an tmpfs(no uuid), and with_fsid==0,
this function test_export still return 1 (write success). that's wrong.

2. and another problem: validate_export() just generate log and return void.
We think that validate_export() should return an int value to indicate whether the path can export. And in export_all(), should not export the path if invalid;

static void
export_all(int verbose)
{
        nfs_export      *exp;
        int             i;

        for (i = 0; i < MCL_MAXTYPES; i++) {
                for (exp = exportlist[i].p_head; exp; exp = exp->m_next) {
                        if (verbose)
                                printf("exporting %s:%s\n",
                                       exp->m_client->m_hostname,
                                       exp->m_export.e_path);
                        exp->m_xtabent = 1;
                        exp->m_mayexport = 1;
                        exp->m_changed = 1;
                        exp->m_warned = 0;
                        validate_export(exp);
                }
        }
}


static void <<<- should return int value to indicate whether the path can export
validate_export(nfs_export *exp)
{

#BEGIN
--- exportfs.c	2013-06-06 15:12:58.881567360 +0800
+++ exportfs.c.new	2013-09-14 14:50:56.719877598 +0800
@@ -475,6 +475,9 @@ validate_export(nfs_export *exp)
 			xlog(L_ERROR, "%s does not support NFS export", path);
 		return;
 
+	} else {
+		xlog(L_ERROR, "Assert: test_export() %s fail", path);
+		return;
 	}
 }

#END

this patch could avoid the test_export work fail.

This request was not resolved in time for the current release.
Red Hat invites you to ask your support representative to
propose this request, if still desired, for consideration in
the next release of Red Hat Enterprise Linux.

(In reply to Yin.JianHong from comment #0)
> +++ This bug was initially created as a clone of Bug #1007626 +++
> 
>
This was closed as WONTFIX so I'm going to do wit this one.