Quoted from the download page:
IMPORTANT ERRATA ADDENDUM: Using the installer on a multi-slice disk will improperly resize the target slice when it is not the last slice, to be the same size as the last slice, leading to a corrupt disk! We will have an update to fix this problem in the next 24 hours!
Well, Im affected by this bug, all my disk partitions goes to dump… but, It´s good, now I only have DragonFly BSD installed and GOD ! It´s awesome ! Keep up good work :D.