# Pari error when factoring polynomial

I ran the following code to factor a polynomial over a number field:

```
U.<z> = CyclotomicField(32)
P.<x> = PolynomialRing(U)
f = x^16-256
print f.factor()
```

This code works for all substitutions of 256 by another value I have tried, but this one gives an error:

```
Traceback (most recent call last):
File "p_is_2_test.sage.py", line 10, in <module>
print f.factor()
File "sage/rings/polynomial/polynomial_element.pyx", line 4199, in sage.rings.polynomial.polynomial_element.Polynomial.factor (build/cythonized/sage/rings/polynomial/polynomial_element.c:39418)
File "cypari2/auto_gen.pxi", line 17246, in cypari2.gen.Gen_auto.nffactor
File "cypari2/handle_error.pyx", line 196, in cypari2.handle_error._pari_err_handle
cypari2.handle_error.PariError: inconsistent concatenation t_COL (8 elts) , t_VEC (8 elts)
```

This seems like some bug in sage, but I am not quite sure what to make of the error. Does anyone know how to deal with this error and to properly let sage factor this polynomial?