install failed because a dependencies modules but i had already installed this modules

[MengxuanXia]

Dear author
cpanminus is an useful tools to install perl modules, but I meet some questions.
When I install PDF::API2 by using cpanm --reinstall --mirror http://mirrors.163.com/cpan/ PDF::API2
It reported that

--> Working on PDF::API2
Fetching http://mirrors.163.com/cpan/authors/id/S/SS/SSIMMS/PDF-API2-2.040.tar.gz ... OK
Configuring PDF-API2-2.040 ... OK
==> Found dependencies: Test::Exception, Test::Memory::Cycle
--> Working on Test::Exception
Fetching http://mirrors.163.com/cpan/authors/id/E/EX/EXODIST/Test-Exception-0.43.tar.gz ... OK
Configuring Test-Exception-0.43 ... OK
Building and testing Test-Exception-0.43 ... OK
Successfully installed Test-Exception-0.43
--> Working on Test::Memory::Cycle
Fetching http://mirrors.163.com/cpan/authors/id/P/PE/PETDANCE/Test-Memory-Cycle-1.06.tar.gz ... OK
Configuring Test-Memory-Cycle-1.06 ... OK
==> Found dependencies: PadWalker
--> Working on PadWalker
Fetching http://mirrors.163.com/cpan/authors/id/R/RO/ROBIN/PadWalker-2.5.tar.gz ... OK
Configuring PadWalker-2.5 ... OK
Building and testing PadWalker-2.5 ... OK
Successfully installed PadWalker-2.5
! Installing the dependencies failed: Module 'PadWalker' is not installed
! Bailing out the installation for Test-Memory-Cycle-1.06.
! Installing the dependencies failed: Module 'Test::Memory::Cycle' is not installed, Module 'Test::Exception' is not installed
! Bailing out the installation for PDF-API2-2.040.
2 distributions installed

       Then I install PadWalker by using **cpanm  --mirror http://mirrors.163.com/cpan/ PadWalker**  
       It reported that 

--> Working on PadWalker
Fetching http://mirrors.163.com/cpan/authors/id/R/RO/ROBIN/PadWalker-2.5.tar.gz ... OK
Configuring PadWalker-2.5 ... OK
Building and testing PadWalker-2.5 ... OK
Successfully installed PadWalker-2.5
1 distribution installed

        When I reinstall PDF::API2 by same line, it also reported that PadWalker not installed
        What's wrong?  thank you