Parece que resolvo esse problema. Eu deveria usar valores digitais em vez de porcentagem.
# Partitioning
# use first hard drive SCSI/SATA:
d-i partman-auto/disk string /dev/sda
d-i partman-auto/method string regular
d-i partman-auto/purge_lvm_from_device boolean true
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-md/device_remove_md boolean true
d-i partman-lvm/confirm boolean true
d-i partman-auto/choose_recipe select atomic
# Actualy use 50% for / and rest 50% for /TMP
d-i partman-auto/expert_recipe string \
boot-root :: \
2048 30720 1000000000 ext4 \
$primary{ } \
method{ format } format{ } \
use_filesystem{ } filesystem{ ext4 } \
mountpoint{ / } \
. \
50% 4096 50% linux-swap \
method{ swap } format{ } \
. \
2048 30720 -1 ext4 \
method{ format } format{ } \
use_filesystem{ } filesystem{ ext4 } \
mountpoint{ /TMP } \
. \
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true