Comment # 5 on bug 927712 from Neil Rickert

I see the messages.

I'm using encrypted LVM on a bare metal install.  Shutdown is fast.  From the
time the plymouth splash appears until power-off is at most 2 seconds.  I do
see the two message, though there isn't time to read them in full.

No, the file system is not corrupted by this.  My understanding is that the
root file system is remounted as read-only before the final stages of shutdown.
 So a failure to unmount a read-only file system should not cause problems.  I
see it as a message to be ignored.  However, I have not used in virtualbox, so
I am guessing the problem might be there (if there is an actual problem).