The daemon passed "-f" to userdel together with "-r", when the user's files should be removed as well.

However, -f also overrides the check whether the user has any current processes.

If "-f" is wanted for its effects on file removal, it should be used always to get consistent behavior with regard to the other things that "-f" does.  If the other things are not wanted, it shouldn't be used with "-r" either.

I can't really say whether "-f" should always be used or never, though.

(Maybe userdel needs fixing so that it doesn't overload -f with so many things.)