Pourquoi cpanm échoue-t-il sur les distributions sans makefiles appropriés où cpan -i réussit ?

Je suis sur Strawberry Perl sur Windows 7 64-bit. cpanm échoue comme ça pour de nombreux paquets dans cpan :

$ cpanm Getopt::Long::Descriptive
Fetching http://www.cpan.org/authors/id/R/RJ/RJBS/Getopt-Long-Descriptive-0.097.tar.gz ... OK
Configuring Getopt-Long-Descriptive-0.097 ... N/A
! The distribution doesn't have a proper Makefile.PL/Build.PL See C:\Users\me\.cpanm\work\1399608810.1056\build.log for details.

Pourtant, cpan -i Getopt::Long::Descriptive réussit. Vous savez pourquoi ?

EDIT (sortie build.log)

cpanm (App::cpanminus) 1.7001 on perl 5.018002 built for MSWin32-x64-multi-thread
Work directory is C:\Users\me/.cpanm/work/1399608810.1056
You have make C:\strawberry\c\bin\dmake.exe
You have LWP 6.05
You have C:\dev\tools\UnxUtils\usr\local\wbin\tar.exe, C:\dev\tools\UnxUtils\usr\local\wbin\gzip.exe and C:\dev\tools\UnxUtils\usr\local\wbin\bzip2.exe
You have C:\dev\tools\UnxUtils\usr\local\wbin\unzip.exe
Searching Getopt::Long::Descriptive on cpanmetadb ...
--> Working on Getopt::Long::Descriptive
Fetching http://www.cpan.org/authors/id/R/RJ/RJBS/Getopt-Long-Descriptive-0.097.tar.gz
-> OK
Unpacking Getopt-Long-Descriptive-0.097.tar.gz
Entering Getopt-Long-Descriptive-0.097
META.yml/json not found. Creating skeleton for it.
Configuring Getopt-Long-Descriptive-0.097
-> N/A
-> FAIL The distribution doesn't have a proper Makefile.PL/Build.PL See C:\Users\me\.cpanm\work\1399608810.1056\build.log for details.

EDIT (problème de déballage)

Fascinant, il semble que les fichiers soient décompressés, mais n'apparaissent jamais sur le disque !

C:\Users\me>cpanm -v --look Getopt::Long::Descriptive
cpanm (App::cpanminus) 1.5018 on perl 5.016002 built for MSWin32-x64-multi-thread
Work directory is C:\Users\me/.cpanm/work/1399909160.7264
You have make C:\strawberry\c\bin\dmake.exe
You have LWP 6.04
You have C:\UnxUtils\usr\local\wbin\tar.exe, C:\UnxUtils\usr\local\wbin\gzip.exe and C:\UnxUtils\usr\local\wbin\bzip2.exe
You have C:\UnxUtils\usr\local\wbin\unzip.exe
Searching Getopt::Long::Descriptive on cpanmetadb ...
--> Working on Getopt::Long::Descriptive
Fetching http://www.cpan.org/authors/id/R/RJ/RJBS/Getopt-Long-Descriptive-0.097.tar.gz ... OK
Unpacking Getopt-Long-Descriptive-0.097.tar.gz
Getopt-Long-Descriptive-0.097
README
Changes
LICENSE
dist.ini
META.yml
MANIFEST
META.json
Makefile.PL
t
descriptive.t
shortcircuit.t
release
pod-syntax.t
000-report-versions-tiny.t
Long
Descriptive.pm
changes_has_content.t
Descriptive
Opts.pm
Usage.pm
Entering Getopt-Long-Descriptive-0.097
Entering C:/Users/me/.cpanm/work/1399909160.7264/Getopt-Long-Descriptive-0.097 with C:\Windows\system32\cmd.exe
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\me\.cpanm\work\1399909160.7264\Getopt-Long-Descriptive-0.097>dir
 Volume in drive C is OS
 Volume Serial Number is 008E-DBB0

 Directory of C:\Users\me\.cpanm\work\1399909160.7264\Getopt-Long-Descriptive-0.097

05/12/2014  11:39 AM    <DIR>          .
05/12/2014  11:39 AM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)  48,360,112,128 bytes free

EDIT (fichiers trouvés, remonter d'un niveau)

C:\Users\me\.cpanm\work\1399909160.7264\Getopt-Long-Descriptive-0.097>cd ..

C:\Users\me\.cpanm\work\1399909160.7264>ls
000-report-versions-tiny.t            Makefile.PL
Changes                               Opts.pm
Descriptive                           README
Descriptive.pm                        Usage.pm
Getopt-Long-Descriptive-0.097         changes_has_content.t
Getopt-Long-Descriptive-0.097.tar.gz  descriptive.t
LICENSE                               dist.ini
Long                                  pod-syntax.t
MANIFEST                              release
META.json                             shortcircuit.t
META.yml                              t