More wording tweak. Members are sorted only in source dims (for now).

sc/qa/unit/ucalc.cxx

@@ -1904,9 +1904,10 @@ void Test::testPivotTableCache()
     aDimName = aCache.GetDimensionName(2);
     CPPUNIT_ASSERT_MESSAGE("wrong dimension name", aDimName.equalsAscii("F3"));
 
-    // In each dimension, member ID values also represent their sort order.
-    // Value items are sorted before string ones.  Also, no duplicate
-    // dimension members should exist.
+    // In each dimension, member ID values also represent their sort order (in
+    // source dimensions only, not in group dimensions). Value items are
+    // sorted before string ones. Also, no duplicate dimension members should
+    // exist.
 
     // Dimension 0 - a mix of strings and values.
     long nMemCount = aCache.GetDimMemberCount(0);