bug in x1=Mod(x+X,X^2+1)^2?

Is this a bug?

? x1=Mod(x+X,X^2+1)^2
%11 = Mod(1, X^2 + 1)*x^2 + Mod(2*X, X^2 + 1)*x + Mod(-1, X^2 + 1)
? x2=Mod(X+x,x^2+1)^2
%12 = Mod(2*X*x + (X^2 - 1), x^2 + 1)
? norm(x2)
%13 = X^4 + 2*X^2 + 1
? norm(x1)
  ***   at top-level: norm(x1)
  ***                 ^--------
  *** norm: incorrect type in greal/gimag (t_POLMOD).