Why do these two loops produce different output?

#! perl -slw
use strict;

print "Loop 1";
A: for my $a ( 0 .. 9 ) {
    $a % $_ or next A for 2..4;
    print $a;
}

print "\nLoop 2";
B: for my $a ( 0 .. 9 ) {
    for my $b ( 2..4 ) {
        unless( $a % $b ) {
            next B;
        }
        else {
            print $a;
        }
    }
}
__END__
C:\test>junk48
Loop 1
1
5
7

Loop 2
1
1
1
3
5
5
5
7
7
7
9
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