diff -r 416cd57d38cf Lib/idlelib/IOBinding.py
--- a/Lib/idlelib/IOBinding.py	Sun Jul 15 00:38:43 2012 +1000
+++ b/Lib/idlelib/IOBinding.py	Sun Jul 15 19:05:12 2012 -0500
@@ -497,15 +497,19 @@
 
     def defaultfilename(self, mode="open"):
         if self.filename:
-            return os.path.split(self.filename)
+            dir, base = os.path.split(self.filename)
         elif self.dirname:
-            return self.dirname, ""
+            dir, base = self.dirname, ""
         else:
             try:
                 pwd = os.getcwd()
             except os.error:
                 pwd = ""
-            return pwd, ""
+            dir, base = pwd, ""
+        if base.startswith('~') and sys.platform[:3] == 'win':
+            # Fix Tcl/Tk Tilde Substitution problem on Windows
+            base = '\\' + base  # escape the tilde
+        return dir, base
 
     def asksavefile(self):
         dir, base = self.defaultfilename("save")