Quick and messy, but here are some examples: (works)

#!/usr/bin/perl

use Win32::GUI;

my $w = 800; my $h = 800; my $i;
$main = Win32::GUI::Window->new(
    -name         => 'main',
    -width        => $w,
    -height        => $h,
    -menu        => $menu,
);

$main->AddButton(
    -height        => 20,
    -width        => 100,
    -text            => 'Go!',
    -name        => 'execute',
    -top            => 20,
    -left            => 650,
    -tabstop     => 1,
);

$main->Show();
Win32::GUI::Dialog();

sub another_sub {
    $top = 50;
    for ($x = 0; $x <= 2; $x++) {
        $uniqueWindow[$i] = $main->AddTextfield(
            -height            => 200,
            -width            => $w-30,
            -background    => [255,255,255],
            -top                => $top,
            -left                => 10,
            -text                => "",
            -name            => $i."Textfield",
            -align                => left,
            -readonly         => 1,
            -multiline        => 1,
            -autovscroll     => 1,
            -vscroll            => 1,
        );
        $uniqueWindow[$i]->SetLimitText(1000);
        $top+=205; $i++;
    }
}

sub execute_Click {
    another_sub();
    foreach $j (0..$i-1) {
        $SUB = $j."Textfield_MaxText";
        print "-->Assigning sub function for $j\n";
        my $idx = $j; # make a copy
        my $SUB = "${idx}Textfield_MaxText";
        *$SUB = sub { variableMaxText( $idx ); }
    } 
    for ($x=0;$x<100;$x++) {
        foreach my $txt (0..$i-1) {
            $uniqueWindow[$txt]->Append("Characters to make it overflo
+w");
        }
    }
}

sub variableMaxText {
    my ($self) = $_[0];
    print "Variable window got maxtexted ($self).\n";
    $uniqueWindow[$self]->Text("");
}
[download]

And I think it should, but it doesn't (minor change, didn't include everything)

    foreach $j (0..$i-1) {
        $SUB = $j."Textfield_MaxText";
        print "-->Assigning sub function for $j\n";
        my $SUB = "${idx}Textfield_MaxText";
        *$SUB = sub { variableMaxText( $j ); }
    }
[download]

Output from the success:

-->Assigning sub function for 0
-->Assigning sub function for 1
-->Assigning sub function for 2
Variable window got maxtexted (1).
Variable window got maxtexted (2).
Variable window got maxtexted (1).
Variable window got maxtexted (2).
[download]

Output from the failure:

-->Assigning sub function for 0
-->Assigning sub function for 1
-->Assigning sub function for 2
Variable window got maxtexted ().
Variable window got maxtexted ().
[download]

And if we get crazy and assign my $j where I define my $i:

-->Assigning sub function for 0
-->Assigning sub function for 1
-->Assigning sub function for 2
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
Variable window got maxtexted (2).
[download]