### Vector over a polynomial ring

In Sage 6.3 (both command line and notebook), I tried to define a vector over Q[X] as follows

```
R = PolynomialRing(QQ,'x')
X = polygen(R)
a, b = X^4-1, X-1
vec = vector(R,[a, b])
```

This produces an error

```
TypeError: not a constant polynomial
```

By contrast, the following works:

```
sage: vec = vector(R,[[a],[b]])
sage: vec
(x^4 - 1, x - 1)
```

Is this a bug or could someone explain me why?