Password requirement "Must contain letters and numbers" is not working properly

ACP > User registration settings > Password complexity
The description says: "subsequent options include the previous ones"

• No requirements --> Any characters
• Must be mixed case --> Both uppercase and lowercase letter
• Must contain letters and numbers: As for the description said, the password should contain: uppercase letters, lowercase letters and numbers. But it works also using only uppercase letters and numbers or lowercase letters and numbers.

Therefore, I think there is a bug or the description should be more precise. The next level (symbols) seems to be correct: it requires uppercase letters, lowercase letters, numbers and symbols.

Thank you in advance!