Index: src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFRichTextString.java
===================================================================
--- src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFRichTextString.java	(revisión: 1765824)
+++ src/ooxml/java/org/apache/poi/xssf/usermodel/XSSFRichTextString.java	(copia de trabajo)
@@ -75,7 +75,7 @@
  * </blockquote>
  */
 public class XSSFRichTextString implements RichTextString {
-    private static final Pattern utfPtrn = Pattern.compile("_x([0-9A-F]{4})_");
+    private static final Pattern utfPtrn = Pattern.compile("_x([0-9A-Fa-f]{4})_");
 
     private CTRst st;
     private StylesTable styles;
Index: src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFRichTextString.java
===================================================================
--- src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFRichTextString.java	(revisión: 1765824)
+++ src/ooxml/testcases/org/apache/poi/xssf/usermodel/TestXSSFRichTextString.java	(copia de trabajo)
@@ -236,6 +236,11 @@
         //_x000D_ is converted into carriage return
         assertEquals("abc\r2ef\r", rt.getString());
         
+	// Test Lowercase case
+	CTRst st2 = CTRst.Factory.newInstance();
+	st2.setT("abc_x000d_2ef_x000d_");
+	XSSFRichTextString rt2 = new XSSFRichTextString(st2);
+	assertEquals("abc\r2ef\r", rt2.getString());
     }
 
     public void testApplyFont_lowlevel(){