U-boot problem on ZYXEL 2812

If have installed the latest snapshot version from Lede. My router is a ZyXel 2812 F1.
My router will be connected to an ADSL line.
To do so I changed in /etc/config/network

config dsl 'dsl'
option annex 'a'
option tone 'av'
option xfer_mode 'ptm'

to

config dsl 'dsl'
option annex 'a'
option tone 'av'
option xfer_mode 'atm'

After I have done that I can reboot from CLI once. If I reboot from CLI again I get:
U-Boot SPL 2013.10-openwrt5 (Nov 18 2014 - 19:54:01)
SPL: initializing NAND flash
SPL: checking U-Boot image
SPL: loading U-Boot to RAM
SPL: decompressing U-Boot with LZO
SPL: cannot start U-Boot

I can only reboot with power off/on.

After changing back to 'ptm' I can reboot from CLI normal after tthe second reboot.

Is there no VDLS.bin needed for this config?