Creation of a polynomial over QQbar

[tmonteil]

Here is the issue: there is no problem buildind a polynomial over AA:

sage: R = AA[x]                       
sage: P = R(x^6+x^5+x^4-x^3+x^2-x+2/5)

But the same operation does not work on QQbar:

sage: S = QQbar[x]
sage: Q = S(x^6+x^5+x^4-x^3+x^2-x+2/5)
Traceback (most recent call last)
...
NotImplementedError: symbol

Hovewer, this workaround works:

sage: Q = P.change_ring(QQbar)

Moreover the following works :

sage: S.<x> = PolynomialRing(QQbar,'x')
sage: Q = S(x^6+x^5+x^4-x^3+x^2-x+2/5)
sage: S == QQbar[x]
True

Weird isn't it ?