Correct me if I'm wrong. However, if I am not wrong, I believe it to be a bug.
The identifier $ial(NICK) returns the fulladdress of a nick (NICK!USER@HOST) if it is in the IAL list.
The identifier $address(NICK, 5) would have to return the fulladdress of a nickname as well.
However, I checked that the $address(NICK, 5) returns only the last ten characters of the USER. This problem extends to the identifier $mask.
//echo -a $mask(abcdefghijklmnopqrstuvwxyz!abcdefghijklmnopqrstuvwxyz@abcdefghijklmnopqrstuvwxyz,5)