diff -r 554ead559f24 Lib/turtledemo/__main__.py
--- a/Lib/turtledemo/__main__.py	Thu Sep 04 01:42:29 2014 -0700
+++ b/Lib/turtledemo/__main__.py	Thu Sep 04 17:04:32 2014 +0300
@@ -214,6 +214,9 @@
         text['font'] = tuple(txtfont)
         text['yscrollcommand'] = vbar.set
         text['xscrollcommand'] = hbar.set
+        text.bind('<Control-MouseWheel>', self.update_mousewheel)
+        text.bind('<Control-Button-4>', self.increase_size)
+        text.bind('<Control-Button-5>', self.decrease_size)
         text.pack(side=LEFT, fill=BOTH, expand=1)
         return text_frame
 
@@ -241,9 +244,6 @@
         widget.bind_all('<%s-underscore>' % shortcut, self.decrease_size)
         widget.bind_all('<%s-equal>' % shortcut, self.increase_size)
         widget.bind_all('<%s-plus>' % shortcut, self.increase_size)
-        widget.bind_all('<Control-MouseWheel>', self.update_mousewheel)
-        widget.bind('<Control-Button-4>', self.increase_size)
-        widget.bind('<Control-Button-5>', self.decrease_size)
 
     def set_txtsize(self, size):
         txtfont[1] = size
@@ -252,15 +252,19 @@
 
     def decrease_size(self, dummy=None):
         self.set_txtsize(max(txtfont[1] - 1, MINIMUM_FONT_SIZE))
+        return 'break'
 
     def increase_size(self, dummy=None):
         self.set_txtsize(min(txtfont[1] + 1, MAXIMUM_FONT_SIZE))
+        return 'break'
 
     def update_mousewheel(self, event):
         # For wheel up, event.delte = 120 on Windows, -1 on darwin.
         # X-11 sends Control-Button-4 event instead.
-        (self.decrease_size() if (event.delta < 0 and not darwin)
-            else self.increase_size())
+        if (event.delta < 0) == (not darwin):
+            return self.decrease_size()
+        else:
+            return self.increase_size()
 
     def configGUI(self, start, stop, clear, txt="", color="blue"):
         self.start_btn.config(state=start,