Default [Q] Backup/restore question with TWRP

Since I have SlimKat ROM, I have TWRP installed as recovery, but I am wondering if my backups are complete: this version of TWRP does not seem to backup .android_secure. The same for restore: .android_restore is not handled
Why ? I saw some videos with TWRP 2.1.1 that shows .android_restore partition in backup/restore screens