@@ -49,9 +49,10 @@ def test_truncate(self):
         f.seek(10)
         f.truncate()
         eq(f.getvalue(), 'abcdefghij')
-        f.seek(0)
         f.truncate(5)
         eq(f.getvalue(), 'abcde')
+        f.write('xyz')
+        eq(f.getvalue(), 'abcdexyz')
         f.close()
         self.assertRaises(ValueError, f.write, 'frobnitz')
 
 
@@ -41,6 +41,11 @@ Core and builtins
 Extension modules
 -----------------
 
+- Patch 1012740:  truncate() on a writeable cStringIO now resets the
+  position to the end of the stream.  This is consistent with the original
+  StringIO module and avoids inadvertently resurrecting data that was
+  supposed to have been truncated away.
+
 - Added socket.socketpair().
 
 Library
@@ -59,7 +64,7 @@ Library
 - A new function tkFont.nametofont was added to return an existing
   font. The Font class constructor now has an additional exists argument
   which, if True, requests to return/configure an existing font, rather
-  than creating a new one. 
+  than creating a new one.
 
 - Updated the decimal package's min() and max() methods to match the
   latest revision of the General Decimal Arithmetic Specification.
 
@@ -289,6 +289,7 @@ IO_truncate(IOobject *self, PyObject *args) {
         if (pos < 0) pos = self->pos;
 
         if (self->string_size > pos) self->string_size = pos;
+        self->pos = self->string_size;
 
         Py_INCREF(Py_None);
         return Py_None;