setcodepage to cp_none causes concatenation failure (windows only)

Summary

A simple program below illustrates the problem. Setting an ansistring codepage to cp_none causes concatenation with a string with a different codepage to fail with the cp_none string ignore. This behaviour is observed only under Windows.

System Information

Windows-11 FPC 3.2.2 (as distributed with Lazarus) x86_64 Desktop environment

Steps to reproduce

Compile and run the simple program given below.

Example Project

Program project1;

uses Sysutils;

const
  sTest = 'Test';

var s1: RawByteString;
    s2, s3: AnsiString;
begin
  writeln('Case #1: s1 code page = utf8');
  SetString(s1,PAnsiChar(sTest),length(sTest));
  SetCodePage(s1,cp_utf8,false);
  writeln('s1 Codepage = ',StringCodePage(s1),', Len = ',Length(s1),' Value = ',s1);
  s2 := IntToStr(1);
  writeln('s2 Codepage = ',StringCodePage(s2),', Len = ',Length(s2),' Value = ',s2);
  s3 := s1 + s2;
  writeln('s3 Codepage = ',StringCodePage(s3),', Len = ',Length(s3),' Value = ',s3);
  writeln;

  writeln('Case #2: s1 code page = none');
  SetString(s1,PAnsiChar(sTest),length(sTest));
  SetCodePage(s1,cp_none,false);
  writeln('s1 Codepage = ',StringCodePage(s1),', Len = ',Length(s1),' Value = ',s1);
  s2 := IntToStr(1);
  writeln('s2 Codepage = ',StringCodePage(s2),', Len = ',Length(s2),' Value = ',s2);
  s3 := s1 + s2;
  writeln('s3 Codepage = ',StringCodePage(s3),', Len = ',Length(s3),' Value = ',s3);
  writeln;
  write('Press any key to continue');
  readln;
end.

What is the current bug behavior?

Under Linux, the result is:

Case #1: s1 code page = utf8
s1 Codepage = 65001, Len = 4 Value = Test
s2 Codepage = 0, Len = 1 Value = 1
s3 Codepage = 0, Len = 5 Value = Test1

Case #2: s1 code page = none
s1 Codepage = 65535, Len = 4 Value = Test
s2 Codepage = 0, Len = 1 Value = 1
s3 Codepage = 0, Len = 5 Value = Test1

Under Windows, the result is:

Case #1: s1 code page = utf8
s1 Codepage = 65001, Len = 4 Value = Test
s2 Codepage = 0, Len = 1 Value = 1
s3 Codepage = 1252, Len = 5 Value = Test1

Case #2: s1 code page = none
s1 Codepage = 65535, Len = 4 Value = Test
s2 Codepage = 0, Len = 1 Value = 1
s3 Codepage = 1252, Len = 1 Value = 1

What is the expected (correct) behavior?

In Case #2, the line beginning s3... shows the correct result for Linux, while under Windows an incorrect result is observed.

Relevant logs and/or screenshots

n/a

Possible fixes

?