Yes, it may cause flash incorrect partitions, there's workaround:
In file /lib/upgrade/platform.sh
change section:
zyxel,nbg7815)
kernelname="0:HLOS_1"
rootfsname="rootfs_1"
mmc_do_upgrade "$1"
;;
to
zyxel,nbg7815)
kernelname="0:HLOS"
rootfsname="rootfs"
mmc_do_upgrade "$1"
;;