I don't know why, sorry, but I can confirm it's probably a bug in your build. It doesn't affect my ActivePerl builds. I simplified your code to 

use File::Spec::Win32;
my $wdir = 'C:/strawberry';
$wdir =~ s[:][]g;
$wdir =~ /(.*)/;
print File::Spec::Win32->catfile('C:/cache', $1), "\n";

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and I get (ActivePerl 5.8.8 & 5.10.0) 

C:\cache\C\strawberry

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You presumably get 

C:\cache\C:

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In reply to Re^3: Tainting problem on Strawberry perl by ikegami
in thread Tainting problem on Strawberry perl by EvanCarroll

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