mysql-5.1-5.1.49/sql-common/client.c contains (amongst others):

|        case 27:
|          if (opt_arg)
|            options->max_allowed_packet= atoi(opt_arg);
|          break;

This allows max_allow_packet to be specified as found in the attached file,
but ONLY as a plain integer and NOT in the common notation eg. "100M" used
elsewhere in my.cnf (which is parsed via mysys/my_getopt.c).

This difference in parsing can create quite an amount of confusion and
should therefore clearly be stated (at least) in the configuration
template.