bug in gsincos?

[Ilya Zakharevich <ilya@math.ohio-state.edu>]

? sin(x+x*y)
%1 = (y + 1)*x + (-1/6*y^3 - 1/2*y^2 - 1/2*y - 1/6)*x^3 + (1/120*y^5 +
1/24*y^4 + 1/12*y^3 + 1/12*y^2 + 1/24*y + 1/120)*x^5 + (-1/5040*y^7 -
1/720*y^6 - 1/240*y^5 - 1/144*y^4 - 1/144*y^3 - 1/240*y^2 - 1/720*y -
1/5040)*x^7 + (1/362880*y^9 + 1/40320*y^8 + 1/10080*y^7 + 1/4320*y^6 +
1/2880*y^5 + 1/2880*y^4 + 1/4320*y^3 + 1/10080*y^2 + 1/40320*y +
1/362880)*x^9 + (-1/39916800*y^11 - 1/3628800*y^10 - 1/725760*y^9 -
1/241920*y^8 - 1/120960*y^7 - 1/86400*y^6 - 1/86400*y^5 - 1/120960*y^4
- 1/241920*y^3 - 1/725760*y^2 - 1/3628800*y - 1/39916800)*x^11 +
(1/6227020800*y^13 + 1/479001600*y^12 + 1/79833600*y^11 +
1/21772800*y^10 + 1/8709120*y^9 + 1/4838400*y^8 + 1/3628800*y^7 +
1/3628800*y^6 + 1/4838400*y^5 + 1/8709120*y^4 + 1/21772800*y^3 +
1/79833600*y^2 + 1/479001600*y + 1/6227020800)*x^13 +
(-1/1307674368000*y^15 - 1/87178291200*y^14 - 1/12454041600*y^13 -
1/2874009600*y^12 - 1/958003200*y^11 - 1/435456000*y^10 -
1/261273600*y^9 - 1/203212800*y^8 - 1/203212800*y^7 - 1/261273600*y^6
- 1/435456000*y^5 - 1/958003200*y^4 - 1/2874009600*y^3 -
1/12454041600*y^2 - 1/87178291200*y - 1/1307674368000)*x^15 + O(x^16)

? sin(x+y)
  ***   incorrect type in gsincos.

I think the latter result is a bug.  Do not we allow power series with
coefficients being power series?

Ilya