[perl #128184] utf8-c8 is not reversable: encode/decode mismatch

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# New Ticket Created by  H. Merijn Brand 
# Please include the string:  [perl #128184]
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# <URL: https://rt.perl.org/Ticket/Display.html?id=128184 >


Two issues

I use this to test:
--8<---
#!perl6

use v6;

use Test;

for ^32 {

    say "";
    say $_;

    my @data = ^20 .map({ 256.rand.Int }).list;
    @data.unshift: 61;

    #dd @data;

    my $b = Buf.new(@data);

    ok((my Str $u = $b.decode("utf8-c8")), "decode");

    my @back = $u.encode("utf8-c8").list;

    #dd @back;

    my $n = Buf.new(@back);

    is-deeply($n, $b, "Data");
    }
-->8---

First issue is that the buffer returns something longer than the original (a \0 
is added):

# expected: 
Buf.new(61,29,61,200,30,99,107,150,71,11,253,134,110,27,35,227,88,140,180,158,209)
#      got: 
Buf.new(61,29,61,200,30,99,107,150,71,11,253,134,110,27,35,227,88,140,180,158,209,0)

# expected: 
Buf.new(61,2,71,91,58,252,6,247,88,58,121,32,124,129,191,126,36,222,185,109,213)
#      got: 
Buf.new(61,2,71,91,58,252,6,247,88,58,121,32,124,129,191,126,36,222,185,109,213,0)

The second issue is more fun, pairs are swapped:

# expected: 
Buf.new(61,147,135,8,82,78,208,66,205,164,204,162,140,97,175,37,108,194,27,192,119)
#      got: 
Buf.new(61,147,135,8,82,78,208,66,204,162,205,164,140,97,175,37,108,194,27,192,119)

205,164,204,162 => 204,162,205,164