Here's the code:

#!/usr/bin/perl

use strict;
use warnings;
use DBI;

######################################################################
+##
package Category;

sub new {
   bless {}, shift;
}

sub load_fromdb {
   my ($self, $dbh) = @_;
   my $query = "SELECT * FROM Category WHERE tag = 'tag'";

   ########## -1- ##########
   print "load_fromdb: got "
     . $dbh->selectall_hashref($query, 'id') . "\n";
}

sub save_todb {
   my ($self, $dbh) = @_;

   ########## -2- ##########
   local $dbh->{RaiseError};

   print "localised \$dbh->{RaiseError}, became "
     . \$dbh->{'RaiseError'} . "\n";
   print "\$dbh is $dbh\n";

   ########## -3- ##########
   my @a = $dbh->selectrow_array("SELECT id FROM Tag WHERE id = 'ciao'
+");
}

######################################################################
+##
package main;

my $dbh =
  DBI->connect("DBI:mysql:database=forecast_recurrent;host=localhost",
   "poletti", "", {'RaiseError' => 0, 'PrintError' => 0});
print "DB handler: $dbh\n";

my $c = new Category;
$c->load_fromdb($dbh, 'HEAD');
print "\$c object holds " . scalar(keys %$c) . " elements\n";
$c->save_todb($dbh, 'TRY');
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which yields:

DB handler: DBI::db=HASH(0x824be28)
load_fromdb: got HASH(0x8231a10)
$c object holds 0 elements
localised $dbh->{RaiseError}, became SCALAR(0x81bf144)
$dbh is DBI::db=HASH(0x824be28)
Attempt to free unreferenced scalar: SV 0x81bf1f8.
[download]

So, the offending SV actually is the localised hash element.

Now, when I comment any line after a numbered comment, the error disappears. I may understand that commenting out the "offending" reference, i.e. line after comment #2, but I really cannot understand the other two!

poletti@flaviox ~> perl -v                                            
+                                    
This is perl, v5.8.6 built for i386-linux

$DBI::VERSION = "1.40"; # From Slackware
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