Edit Group settings for a course, throws error error:

Passwords must be at least 8 characters long.
Passwords must have at least 1 lower case letter(s).
Passwords must have at least 1 non-alphanumeric character(s).

Scenario:

1. I created a new group e.g. G10 with enrollment key E10
2. Once the group is created I clicked on Edit group settings for group G10
3. I changed the key as E9 and got the above error, if I enter the same old key E10, it will save the data but with new key E9 it throws error. Something wrong is going on.

Thanks