Index: wp-testcase/test_includes_formatting.php
===================================================================
--- wp-testcase/test_includes_formatting.php	(revision 662)
+++ wp-testcase/test_includes_formatting.php	(working copy)
@@ -1285,6 +1285,24 @@
 
 		$this->assertEquals( $output, remove_accents( $input ), 'remove_accents from ISO-8859-1 text' );
 	}
+
+	public function test_remove_accents_vowels_diacritic() {
+		$this->knownWPBug(17738);
+
+		// Vowels with diacritic
+		// unmarked
+		$this->assertEquals( 'OoUu', remove_accents( 'ƠơƯư' ) );
+		// grave accent
+		$this->assertEquals( 'AaAaEeOoOoUuYy', remove_accents( 'ẦầẰằỀềỒồỜờỪừỲỳ' ) );
+		// hook
+		$this->assertEquals( 'AaAaAaEeEeIiOoOoOoUuUuYy', remove_accents( 'ẢảẨẩẲẳẺẻỂểỈỉỎỏỔổỞởỦủỬửỶỷ' ) );
+		// tilde
+		$this->assertEquals( 'AaAaEeEeOoOoUuYy', remove_accents( 'ẪẫẴẵẼẽỄễỖỗỠỡỮữỸỹ' ) );
+		// acute accent
+		$this->assertEquals( 'AaAaEeOoOoUu', remove_accents( 'ẤấẮắẾếỐốỚớỨứ' ) );
+		// dot below 
+		$this->assertEquals( 'AaAaAaEeEeIiOoOoOoUuUuYy', remove_accents( 'ẠạẬậẶặẸẹỆệỊịỌọỘộỢợỤụỰựỴỵ' ) );
+	}
 }
 
 ?>