diff -r 03df2c1c6892 Lib/idlelib/EditorWindow.py
--- a/Lib/idlelib/EditorWindow.py	Thu Apr 03 10:31:25 2014 -0400
+++ b/Lib/idlelib/EditorWindow.py	Thu Apr 03 20:58:41 2014 +0530
@@ -735,13 +735,8 @@
         base, ext = os.path.splitext(os.path.basename(filename))
         if os.path.normcase(ext) in (".py", ".pyw"):
             return True
-        try:
-            f = open(filename)
-            line = f.readline()
-            f.close()
-        except IOError:
-            return False
-        return line.startswith('#!') and line.find('python') >= 0
+        line = self.text.get('1.0', '1.0 lineend')
+        return line.startswith('#!') and 'python' in line
 
     def close_hook(self):
         if self.flist:
diff -r 03df2c1c6892 Lib/idlelib/IOBinding.py
--- a/Lib/idlelib/IOBinding.py	Thu Apr 03 10:31:25 2014 -0400
+++ b/Lib/idlelib/IOBinding.py	Thu Apr 03 20:58:41 2014 +0530
@@ -553,9 +553,13 @@
 
     def asksavefile(self):
         dir, base = self.defaultfilename("save")
+        filetypes = self.filetypes
+        if not self.editwin.ispythonsource(self.filename):
+            #See issue21140
+            filetypes[0], filetypes[1] = filetypes[1], filetypes[0]
         if not self.savedialog:
             self.savedialog = tkFileDialog.SaveAs(master=self.text,
-                                                  filetypes=self.filetypes)
+                                                  filetypes=filetypes)
         filename = self.savedialog.show(initialdir=dir, initialfile=base)
         if isinstance(filename, unicode):
             filename = filename.encode(filesystemencoding)
@@ -586,6 +590,8 @@
             self.text.event_generate("<<save-window-as-file>>")
         def save_a_copy(self, event):
             self.text.event_generate("<<save-copy-of-window-as-file>>")
+        def ispythonsource(self, filename):
+            return True #Change to False to mock OutputWindow.
     text = Text(root)
     text.pack()
     text.focus_set()
diff -r 03df2c1c6892 Lib/idlelib/OutputWindow.py
--- a/Lib/idlelib/OutputWindow.py	Thu Apr 03 10:31:25 2014 -0400
+++ b/Lib/idlelib/OutputWindow.py	Thu Apr 03 20:58:41 2014 +0530
@@ -20,7 +20,7 @@
 
     def ispythonsource(self, filename):
         # No colorization needed
-        return 0
+        return False
 
     def short_title(self):
         return "Output"