padding/substr quirk

RolandGunslinger has asked for the wisdom of the Perl Monks concerning the following question:

Take a look at this script;

#!perl
use strict;use warnings;
use Time::localtime;
print "substr month= " . (substr("0" . localtime->mon() + 1, -2)) . "\
+n";
print "substr day= " . (substr("0" . localtime->mday(), -2)) . "\n";
print "sprintf month= " . (sprintf "%02d", localtime->mon() + 1) . "\n
+";
print "sprintf day= " . (sprintf "%02d", localtime->mday()) . "\n";
[download]

It returns the following;

>perl pad.pl
substr month= 1
substr day= 09
sprintf month= 01
sprintf day= 09
[download]

Now, I know the first two lines are not a good way to pad. I found some nodes on Perlmonks that showed a better way, which is the last two lines. The problem is I'm perplexed as to the first result. Why does substr month only return a 1 instead of 01?
I'm using ActiveState Perl 5.8.0 running under Win32. Thanks.

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