Fn+F12(suspend) does not work on T400

Although I can hibernate my Lenovo Thinkpad T400 using the “Suspend to Disk” menu item without any problem, I cannot do the same by pressing the Fn+F12(suspend) keys. The latter displays an error message:
“Could not umount external media before suspend/standby. (Reason: Could not call DCOP interface to umount external media.) Would you like to continue suspend/standby anyway (Warning: Continue suspend can cause data loss!)”

The error messages is erroneous, I have no external media. Moreover, I umounted manually everything I could (including /sys, /sys/kernel/debug, /sys/fs/fuse/connections, /sys/kernel/security, /proc/sys/fs/binfmt_misc, /windows/* and /afs), leaving only the following filesystems mounted:
/dev/sda5 on / type ext3 (rw,acl,user_xattr)
proc on /proc type proc (rw)
udev on /dev type tmpfs (rw)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
/dev/sda6 on /home type ext3 (rw,acl,user_xattr)

Still I get the same error message when I press Fn+F12.
OpenSUSE 11, KDE4, kernel 2.6.25.18-0.2-default x86_64.
What should I do to make Fn+F12 work correctly?

Same bug in openSUSE 11.1.