Index: XSSFSheet.java
===================================================================
--- XSSFSheet.java	(revision 994959)
+++ XSSFSheet.java	(working copy)
@@ -1351,7 +1351,11 @@
                 mergeCellsArray[i - 1] = ctMergeCells.getMergeCellArray(i);
             }
         }
-        ctMergeCells.setMergeCellArray(mergeCellsArray);
+        if(mergeCellsArray.length > 0){
+            ctMergeCells.setMergeCellArray(mergeCellsArray);
+        }else{
+            worksheet.unsetMergeCells();
+        }
     }
 
     /**