Issues changing root password

[tstngry]

After reseting my kindle to factory defaults, and finally figuring out how to ssh back into my kindle, I tried to change the root password by:

mntroot rw
passwd root

However after I do this and restart the kindle to confirm changes have taken effect, the password is still blank. I have tried this many times with different passwords of varying length and each time I can login to the kindle by simply pressing enter. Before reseting my kindle I used the ssh keys which worked fine, I just want to confirm that my root password is changed. Any idea as to why the password changes may not be taking effect? Any help would be greatly appreciated, Thank you.