[newbie] why does ratsimp not work here?



Even though it's easy to simplify the result by hand, I'd like Maxima to 
do it:

g:matrix([1.5,-0.5,-1],[-0.5,0.5+s,-s],[-1,-s,1+s]);
currents:matrix([1],[0],[0]);
u:invert(g).currents;
result:u[2]/u[1];

 				 0.5 (s + 1) + s
(%o66)                     [----------------------]
                                                  2
                             (s + 0.5) (s + 1) - s


which is correct

now I want to simplify this result with ratsimp(result);
but I get the following "error/warning":

`rat' replaced 0.5 by 1/2 = 0.5

`rat' replaced 0.5 by 1/2 = 0.5
  and not the expected expression:
(4s+1)/(2s^2+4s+1)

any help appreciated
hugo