Halted system won't halt

[David Newall <davidn@davidnewall.com>]

I've got a remote machine running ubuntu 2.6.24-19-generic which I ssh
into.  When I said "poweroff -f -p" it strangely came back after a few
seconds.  Perhaps my banging on the keyboard made a difference.  The
same thing happened when I said "halt -f -p".  Sounds like user error to
me, except the log file shows kernel halt messages.  These are the last
n lines logged:

Dec 19 01:48:32 ubuntu -- MARK --
Dec 19 02:08:32 ubuntu -- MARK --
Dec 19 02:18:20 ubuntu kernel: [40201.658595] EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended
Dec 19 02:22:02 ubuntu kernel: [40423.339196] sd 1:0:1:0: [sda] Stopping disk
Dec 19 02:22:03 ubuntu kernel: [40424.243004] System halted.
Dec 19 02:23:33 ubuntu kernel: [40514.506694] sd 1:0:1:0: [sda] Stopping disk
Dec 19 02:23:33 ubuntu kernel: [40514.506748] ata2.01: DISK MIGHT NOT BE SPUN DOWN PROPERLY. UPDATE SHUTDOWN UTILITY
Dec 19 02:23:33 ubuntu kernel: [40514.506756] ata2.01: For more info, visit http://linux-ata.org/shutdown.html
Dec 19 02:23:38 ubuntu kernel: [40519.703866] psmouse.c: Failed to deactivate mouse on isa0060/serio1
Dec 19 02:23:40 ubuntu kernel: [40521.903111] System halted.


I can't explain that.