I recently did an update on my Synaptic.
I notice that my /var increased by 287 Mb.
Had I been using a 'minimum' persistence of 200 Mb,
wouldn't that have made knoppix-data.img unusable on the next boot?
Unusable not but no space left and the update will be corrupt.
Now I tested it by myself. While trying to update you'll get a error message. Reboot fails because there is no space left for UNIONFS.

You have to restart with Knoppix cheatcode
Code:
knoppix noimage
and to delete '/mnt-system/KNOPPIX/knoppix-data.img'