The most simple way to make a example of this issue: Install 15.05.1 stable or 17.01 stable and open 192.168.1.1. It tells you that there is no password set. Go to settings, set a password. Open browser again. It asks you now for the password. Power off the device. Wait 2-3 seconds. Power it on. Password is now lost and device have again factory settings.
This makes lede on this device somehow useless. Would be great if someone could fix this problem.