The QUIT FTP command is not mentioned in the VPM when attempting to reference specific FTP "methods" (or commands) in a Web Access Layer rule, under "Services"
Every command but QUIT is referenced.
The CPL allows you to add the QUIT manually to the same command to the list. See below
This will match now in policy as expected.
If the QUIT command does *not* match an ALLOW policy rule, it does not stop the connection from getting closed. It will just show as being DENIED in policy (depending on other policy rules configured) and the connection will not be closed gracefully.