[FS#468] Firstboot does not work on ZyXEL P-2812HNU-F1 (17.01.0-rc1)

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - anonymous (Mijzelf) 

Attached to Project - LEDE Project
Summary - Firstboot does not work on ZyXEL P-2812HNU-F1 (17.01.0-rc1)
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - After installing lede-17.01.0-rc1-r3042-ec095b5-lantiq-xrx200-P2812HNUF1-squashfs-sysupgrade.bin on top of Chaos-Calmer on my P-2812HNU-F1, it kept it's old config, although I didn't specify that
sysupgrade /tmp/lede.bin

After activating fail-safe I tried to use firstboot to drop the config, but it failed:
root@(none):~# firstboot
This will erase all settings and remove any installed packages. Are you sure? [N/y]
y
/dev/ubi0_1 is not mounted
/dev/ubi0_1 will be erased on next mount
writing /dev/ubi0_1 failed: Operation not permittedAfter rebooting it had kept it's config.

Worked around it with
root@(none):~# mount_root 
switching to ubifs overlay
root@(none):/rom/root# firstboot 
This will erase all settings and remove any installed packages. Are you sure? [N/y]
y
/dev/ubi0_1 is mounted as /overlay, only erasing files

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=468