All the snapshots are a full backup

I use BiT 0.9.26 to back up my /home and an additional folder containing music. However, every snapshot it takes has the size of the backed-up directory. So, it seems to me that the hard links are not working well.

The following is the list of the snapshots I have on an external ext3 drive:

$ sudo du --max-depth=1 -h /media/Freecom250/backintime/
27G /media/Freecom250/backintime/20100521-163702
19G /media/Freecom250/backintime/20100525-130000
15G /media/Freecom250/backintime/20100525-090000

Furthermore, this is the config file located in /root/.config/backintime:

# cat /root/.config/backintime/config
config.version=2
gnome.last_path=/home/al
gnome.main_window.height=536
gnome.main_window.hpaned1=200
gnome.main_window.hpaned2=246
gnome.main_window.width=976
gnome.main_window.x=101
gnome.main_window.y=85
gnome.show_hidden_files=false
snapshots.automatic_backup_mode=10
snapshots.cron.nice=true
snapshots.dont_remove_named_snapshots=true
snapshots.exclude_patterns=*.backup*:*~:/home/al/qBT_dir:/home/al/Scaricati:/home/al/.local/share/Trash:.*
snapshots.expert.per_directory_schedule=false
snapshots.include_folders=/home/al|10:/media/win/myTunes|30:/home/al/.thunderbird|20
snapshots.min_free_space.enabled=true
snapshots.min_free_space.unit=20
snapshots.min_free_space.value=50
snapshots.notify.enabled=true
snapshots.path=/media/Freecom250
snapshots.remove_old_snapshots.enabled=true
snapshots.remove_old_snapshots.unit=80
snapshots.remove_old_snapshots.value=10
snapshots.smart_remove=true

The folders included for the backup are set in the following way:
/home/al/ -> every hour
/home/al/.thunderbird -> every day
/media/win/myTunes -> every week.

I read here (https://answers.launchpad.net/backintime/+question/85442) that enabling the option "schedule per included directory" the hardlinking is broken. Is this my case?