What Jenda is trying to say, what perlnumber (and kennethk ) say, is that you should numify one of your arguments, so write

#~ if( 0+$flag & $job_type ){
#~ if( $flag & 0+$job_type ){
#~ if( 0+$flag & 0+$job_type ){
if( int $flag & int $job_type ){
    $bu = $bj{$flag} ;
    cluck("business_unit: $bu");
}
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