This is weird. I tried that as well, but it doesn't work for me:

Q:\>perl -le "@l=qw(a b c);$b=3;do{local @::{@l};$b=2;print $b};print 
+$b
2
2

Q:\>perl -v

This is perl, v5.8.8 built for MSWin32-x86-multi-thread
(with 50 registered patches, see perl -V for more detail)

Copyright 1987-2006, Larry Wall

Binary build 820 [274739] provided by ActiveState http://www.ActiveSta
+te.com
Built Jan 23 2007 15:57:46

Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using "man perl" or "perldoc perl".  If you have access to
+ the
Internet, point your browser at http://www.perl.org/, the Perl Home Pa
+ge.
[download]

On 5.10.0, it starts working:

G:\Aktivitaeten\IDV\wp2-XML-sst\OUTPUT>perl -le "@l=qw(a b c);$b=3;do{
+local @::{@l};$b=2;print $b};print $b"
2
3

G:\Aktivitaeten\IDV\wp2-XML-sst\OUTPUT>perl -v

This is perl, v5.10.0 built for MSWin32-x86-multi-thread

Copyright 1987-2007, Larry Wall

Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using "man perl" or "perldoc perl".  If you have access to
+ the
Internet, point your browser at http://www.perl.org/, the Perl Home Pa
+ge.
[download]

So, I should test my ideas not with the stock Perl but with my "most recent" Perl available :)