Password requirements

[RodStr]

Have been churning through the manuals, and nothing seems to layout the entire FTP Password requirement scheme.
I see the "3 of 4 lists" rule (Uppercase/lowercase/Numeric/Special-punctuation).
Also logically the username cannot exist within the password, and length requirements.

But why doesn't this work:
User: camdenftp
Pass: C@MD3Nftp

Is the "ftp" a reserved set of characters ?

Is there a list of these reserved characters somewhere if that is the case?

Thanks!

Rod