I see the same behaviour as listed with 5.8.[78] & 5.10.0. Try also Deparse (perl -MO=Deparse file) ...

#  test.pm was used in p.pl.
#
#  perl 5.10.0
package test;
sub Init {
    $[ = 1;
    BEGIN {
        $^H{'$['} = q(1);
    }
    $[;
}
sub test {
    $[ = 0;
    print '($[= 0) array has ' . scalar(@_ . " elements, last index = 
+$#_\n");
}
'???';
test.pm syntax OK


use test;
test::test(1, 2, 3, 4);
test::Init();
test::test(1, 2, 3, 4);
p.pl syntax OK

#  perl 5.8.7
package test;
sub Init {
    $[ = 1;

}
sub test {
    print '($[= 1) array has ' . scalar(@_ . " elements, last index = 
+$#_\n");
}
'???';
test.pm syntax OK


use test;
$[ = 1;
test::test(1, 2, 3, 4);
test::Init();
test::test(1, 2, 3, 4);
p.pl syntax OK
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