The PACK001=HASH(0xa556c4) gives a hint as to why calling WriteMakefile twice doesn't work -- MakeMaker is eeeew

... All I can say. PAR Packer isn't remotely near a normal XS library. You can define macros again in postamble, but the makefile becomes unreadable to mere mortals. No core dual lifes use Module::Build as of Perl 5.12. I wont be the first.

I figured out the problem. EUMM deletes or something, I can't tell whats going on, the MY package methods after inheriting them, see cpan/ExtUtils-MakeMaker/lib/ExtUtils/MakeMaker.pm#l966 in perl.git. Why? I have no idea. Workaround in Makefile.pl below. My problem is resolved.

use 5.010000;
use ExtUtils::MakeMaker;
use Config qw(%Config);
use Data::Dumper;
# See lib/ExtUtils/MakeMaker.pm for details of how to influence
# the contents of the Makefile that is written.

%param =    ( NAME              => 'MM123',
    VERSION_FROM      => 'lib/MM123.pm', # finds $VERSION
    PREREQ_PM         => {}, # e.g., Module::Name => 1.1
    ($] >= 5.005 ?     ## Add these new keywords supported since 5.005
      (ABSTRACT_FROM  => 'lib/MM123.pm', # retrieve abstract from modu
+le
       AUTHOR         => 'A. U. Thor <a.u.thor@a.galaxy.far.far.away>'
+) : ()),
                      # e.g., '-lm'
    DEFINE            => '', # e.g., '-DHAVE_SOMETHING'
    INC               => '-I.', # e.g., '-I. -I/usr/include/other'
);


*MY::postamble = sub {
print "postamble hook worked\n";
return '

# POSTAMBLE WORKED
';
};
WriteMakefile(%param);
*MY::postamble = sub {
print "postamble hook worked\n";
return '

# POSTAMBLE WORKED
';
};
WriteMakefile(%param);
[download]

C:\pl\mmbug>perl makefile.pl
WARNING: Setting ABSTRACT via file 'lib/MM123.pm' failed
 at C:/perl512/lib/ExtUtils/MakeMaker.pm line 583
postamble hook worked
Writing Makefile for MM123
WARNING: Setting ABSTRACT via file 'lib/MM123.pm' failed
 at C:/perl512/lib/ExtUtils/MakeMaker.pm line 583
postamble hook worked
Writing Makefile for MM123

C:\pl\mmbug>
[download]