here the excential part of my program : the "initaldir"-option of getSaveFile/getOpenFile works fine under winnt4 but doesn't work on my linux box

#!/usr/bin/perl -w

use Tk;
use strict;
use warnings;
use English;


my $initialdir;
if ($OSNAME =~ /win/i){
        $initialdir = 'C:\temp';
}
if ($OSNAME =~ /linux|unix|bsd/i){
        $initialdir = '/tmp';
}

my $main = new MainWindow;

my $menubar = $main->Frame(-relief=>"raised",
        -borderwidth=>2);

my $filebutton =
        $menubar->Menubutton(
                -text=>"File",
                -underline => 0
        );

my $filemenu = $filebutton->Menu();

$filebutton->configure(
        -menu=>$filemenu
);

$filemenu->command(
        -command => \&open_choice,
        -label => "Open...",
        -underline => 0
);

$filemenu->command(
        -command => \&save_choice,
        -label => "Save...",
        -underline => 0
);

$filemenu->separator;

$filemenu->command(
        -label => "Exit",
        -command => \&exit_choice,
        -underline => 1
);

my $helpbutton =
        $menubar->Menubutton(
                -text=>"Help",
                -underline => 0
        );

$filebutton->pack(
        -side=>"left"
);

$helpbutton->pack(
        -side=>"right"
);

$menubar->pack(
        -side=>"top",
        -fill=>"x"
);

MainLoop;

sub open_choice {
        my $filename = $main->getOpenFile(
                -defaultextension => "cnf",
                -filetypes => [
                        ['Configuration Files','.cnf'],
                        ['All Files','*']
                ],
                -initialdir=> $initialdir,
        );
        return unless $filename;
        print "Open file $filename\n";
}

sub save_choice {
        my $filename = $main->getSaveFile(
                -defaultextension => "cnf",
                -filetypes => [
                        ['Configuration Files','.cnf'],
                        ['All Files','*']
                ],
                -initialdir => $initialdir,
        );
        return unless $filename;
}
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the output of perl -V is:

Summary of my perl5 (revision 5.0 version 6 subversion 1) configuratio
+n:
  Platform:
    osname=linux, osvers=2.4.16-6mdksmp, archname=i386-linux
    uname='linux bi.mandrakesoft.com 2.4.16-6mdksmp #1 smp sat dec 8 0
+4:02:48 cet 2001 i686 unknown '
    config_args='-des -Darchname=i386-linux -Dd_dosuid -Ud_csh -Dusesh
+rplib -Doptimize=-O3 -fomit-frame-pointer -pipe -mcpu=pentiumpro -mar
+ch=i586 -ffast-math -fno-strength-reduce -Dprefix=/usr -Di_ndbm -Di_g
+dbm -Di_shadow -Di_syslog -Uuselargefiles -Dman1dir=/usr/share/man/ma
+n1 -Dman3dir=/usr/lib/perl5/man/man3'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef usemultipl
+icity=undef
    useperlio=undef d_sfio=undef uselargefiles=undef usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -I/usr/local/include',
    optimize='-O3 -fomit-frame-pointer -pipe -mcpu=pentiumpro -march=i
+586 -ffast-math -fno-strength-reduce',
    cppflags='-fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='2.96 20000731 (Mandrake Linux 8.2 2.96-0
+.75mdk)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=4
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -ldl -lm -lc -lcrypt -lutil
    perllibs=-lnsl -ldl -lm -lc -lcrypt -lutil
    libc=/lib/libc-2.2.4.so, so=so, useshrplib=true, libperl=libperl.s
+o
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynami
+c -Wl,-rpath,/usr/lib/perl5/5.6.1/i386-linux/CORE'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'


Characteristics of this binary (from libperl): 
  Compile-time options:
  Built under linux
  Compiled at Feb 21 2002 01:00:32
  @INC:
    /usr/lib/perl5/5.6.1/i386-linux
    /usr/lib/perl5/5.6.1
    /usr/lib/perl5/site_perl/5.6.1/i386-linux
    /usr/lib/perl5/site_perl/5.6.1
    /usr/lib/perl5/site_perl
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