Index: wp-admin/options-general.php
===================================================================
--- wp-admin/options-general.php	(revision 21103)
+++ wp-admin/options-general.php	(working copy)
@@ -231,12 +231,12 @@
 	<fieldset><legend class="screen-reader-text"><span><?php _e('Date Format') ?></span></legend>
 <?php
 
-	$date_formats = apply_filters( 'date_formats', array(
+	$date_formats = apply_filters( 'date_formats', array_unique( array(
 		__('F j, Y'),
 		'Y/m/d',
 		'm/d/Y',
 		'd/m/Y',
-	) );
+	) ) );
 
 	$custom = true;
 
@@ -264,11 +264,11 @@
 	<fieldset><legend class="screen-reader-text"><span><?php _e('Time Format') ?></span></legend>
 <?php
 
-	$time_formats = apply_filters( 'time_formats', array(
+	$time_formats = apply_filters( 'time_formats', array_unique( array(
 		__('g:i a'),
 		'g:i A',
 		'H:i',
-	) );
+	) ) );
 
 	$custom = true;