i think is a default behaviour if, as i only can guess, in the real script the button is binded is bound to a variable that holds a true value. Your use is more similar to a CheckButton not a Radiobuttom. The inteded use of a Radiobutton is similar to:

my $dot_after = 2;
..
my $fr2 = $scrolled_top->Frame(-borderwidth => 2, -relief => 'groove')
+->pack(-side=>'top',-anchor=>'w',-pady=>5);
  $fr2->Label(-text => "Numbers as dot if ")->pack(-side => 'left',-ex
+pand => 1);
  $fr2->Radiobutton(-text => "1",-variable => \$dot_after, -value=>'1'
+)->pack();
  $fr2->Radiobutton(-text => "2",-variable => \$dot_after, -value=>'2'
+)->pack();
  $fr2->Radiobutton(-text => "3",-variable => \$dot_after, -value=>'3'
+)->pack();
  $fr2->Radiobutton(-text => "4",-variable => \$dot_after, -value=>'4'
+)->pack();
  $fr2->Radiobutton(-text => "never",-variable => \$dot_after, -value=
+>'9999')->pack();
[download]

HtH
L*

Update:typo (en-BAD) fixed,thanks MidLifeXis