diff -r b56ae3f878cb Lib/idlelib/EditorWindow.py
--- a/Lib/idlelib/EditorWindow.py	Mon May 20 22:16:53 2013 -0500
+++ b/Lib/idlelib/EditorWindow.py	Sun May 26 03:25:02 2013 -0500
@@ -596,6 +596,9 @@
         return "break"
 
     def paste(self,event):
+        sel = self.text.tag_ranges("sel")
+        if sel:
+            self.text.delete(*sel)   # issue5124
         self.text.event_generate("<<Paste>>")
         self.text.see("insert")
         return "break"