Ubuntu itself doesn't yet care what the 1st/install user password is, 1 char is allowed.
In the past add users would need to use a min. of 6 chars, now it's at least 7 but not just any 7, has to meet some test (consecutive #'s or horizontal letters on keyboard seem to fail.
Don't really consider a bug, (other than criteria seem weird) but if anyone knows what source controls this would like to know.
(being a poor 2 finger typer typically setup up add users with a simple -
123456 or 234567