an exercise in Comtet's Advanced Combinatorics

[Emeric Deutsch]

Dear Seqfans,
I am checking a statement in Exercise 13 on p. 260 and I do 
not get the desired answer. Just above the table on p. 261, the 
bivariate generating function is given:

> g:=((1-u)*(1-sin(v+t*cos(v)))-1)/(1+u):
> # where u=sin(v) i.e.  
> v:=arcsin(u):
> # I expand g in a series of powers of t:
> g1:=simplify(series(g,t=0,8)):
> # the coefficients of t^n (polynomials in u) do not have nonnegative
coefficients; for example 
> expand(3!*coeff(g1,t^3));

                                      3    4
                         1 - 2 u + 2 u  - u

Am I doing something wrong? I'd appreciate your opinion, I mean help. 
Many thanks.

Emeric