I made mount points for /, /swap and /home and asked it not to format any of them. In the ascii dialog it said it was going to format the / and /home partitions (but not the swap). As this was a clean install, I went ahead and said OK and it happily formatted both those partitions.
I checked for a /var/log/installer/partman file, but it doesn't seem to be there. If there's anything else I can do to help, let me know.
I had the same issue with dapper amd64 beta2.
I made mount points for /, /swap and /home and asked it not to format any of them. In the ascii dialog it said it was going to format the / and /home partitions (but not the swap). As this was a clean install, I went ahead and said OK and it happily formatted both those partitions.
I checked for a /var/log/ installer/ partman file, but it doesn't seem to be there. If there's anything else I can do to help, let me know.