Transliteration operator(tr//)on EBCDIC platform

Hi

I am trying to run this script on an EBCDIC platform using perl-5.8.6
 
($a = "\x89\x8a\x8b\x8c\x8d\x8f\x90\x91") =~ tr/\x89-\x91/X/;
is($a, "XXXXXXXX");


The result I get is 

 'X«»ðý±°X'

a) Is this happening  since \x8a\x8b\x8c\x8d\x8f\x90 are the gapped
characters in EBCDIC ?
or 
b) Should all the bytes in $a change to X?

Thanks in advance
Sastry