Running `mount --move /foo /bar` would leave the old /foo entry in /etc/mtab 
and create a new /bar entry with wrong info.

http://bugs.gentoo.org/104697

--- mount/mount.c
+++ mount/mount.c
@@ -665,6 +665,25 @@
 		else {
 			mntFILE *mfp;
 
+			/* when moving a mount point, we have to make sure the mtab
+			 * gets updated properly.  We get info about the old mount
+			 * point, copy it to the new mount point, and then delete
+			 * the old mount point. */
+			if (flags & MS_MOVE) {
+				const char *olddir = mnt.mnt_fsname;
+				struct mntentchn *oldmc = oldmc = getmntfile(olddir);
+				if (oldmc != NULL) {
+					mnt.mnt_fsname = strdup(oldmc->m.mnt_fsname);
+					mnt.mnt_type = oldmc->m.mnt_type;
+					mnt.mnt_opts = oldmc->m.mnt_opts;
+					mnt.mnt_freq = oldmc->m.mnt_freq;
+					mnt.mnt_passno = oldmc->m.mnt_passno;
+				}
+				update_mtab(olddir, NULL);
+				if (oldmc != NULL)
+					my_free(olddir);
+			}
+
 			lock_mtab();
 			mfp = my_setmntent(MOUNTED, "a+");
 			if (mfp == NULL || mfp->mntent_fp == NULL) {