lprm has an arbitrary limit on the length of the username that can remove
jobs.  

From lprm.c:

static char     luser[16];      /* buffer for person */

void    usage();

int
main(argc, argv)
        int argc;
        char *argv[];
{
        register char *arg;
        struct passwd *p;
        
        uid = getuid();
        euid = geteuid();
        seteuid(uid);
        name = argv[0];
        gethostname(host, sizeof(host));
        host[MAXHOSTNAMELEN-1]='\0';
        openlog("lpd", 0, LOG_LPR);
        if ((p = getpwuid(getuid())) == NULL)
                fatal("Who are you?");
        if (strlen(p->pw_name) >= sizeof(luser))
                fatal("Your name is too long");

[...]

The value of 16 is interesting - why not 9?