bless --nextonly parameter fails

I am using the bless command to reboot my Mac mini into VMware ESX. sudo bless --device /dev/disk3s1 --setboot --nextonly && sudo reboot Booting ESX works but after the next reboot the Mac reboots into ESX again, despite the "--nextonly" parameter. The same command (with a different device) works for rebooting into Windows on the Boot Camp partition once, i.e. after booting into Windows the Mac mini reboots into OS X again. But it doesn't work with booting into ESX. Any ideas? Update: With the --legacy switch the nvram variable is changed to boot from USB and uses the BIOS emulator, which promptly boots from the Windows partition. So that doesn't work.