"This is a development device not intended for production use"

Hello,

After unrooted and re-locked (bootloader) my Nexus 9.
When i boot it, i got this:



"This is a development device not intended for production use"

After that, I have flashed the stock rom 6.0.1,so I'm 100% stock now, but I still get this message when the device boot :eek:

Is it a bug, or my seller sold me a tablet supposed to be not sold? :confused:
Do you think I can ask for a replacement? Because I would like to sell it and buy a other tablet... But with this weird message at the boot, I can't expect a lot from it...


Thanks :)

Download from this link