Hi Xavier,
Today there have been some code pushed to the main repo which was in
i386 but not in x86_64. It is related to the way SMP systems are being
initalized. Would you mind to try with the latest x86_64 ISO snapshot?
Make sure the snapshot is dated on September, 24.
You can grab it from: http://avalon.dragonflybsd.org/snapshots/x86_64/
Cheers,
Antonio Huete